Normally you don't do this, because repelling projectiles actually takes more focus than flinging fireballs or putting up a shield in the first place, but if you can take out all the guns firing on you with their own bullets then you'll get the breather you need.

You refocus the shield and sure enough the bullets are repelled back towards the guns that are firing on you. It isn't an exact hit, but enough of them hit their own guns (or in some cases the gunner) enough that it puts them out of commission, other bullets either go flying off wildly into the air or into other parts of the airship. In any case you hit something that causes problem since you see and hear minor explosions, which the gnomes are probably busily trying to contain. The airship shudders in the sky a bit, but it isn't falling out of sky, which it probably would have done if you'd lobbed hunks of fire at it.

Taking advantage of the respite, your soldiers take what explosives they've found on the bodies of the gnomes, pile them up against the building's door and you hurl a ball of fire at it. Naturally it not only explodes spectacularly, but it also succeeds in destroying a couple of golems that were waiting to ambush you. You and the other run inside, before the airship above you manages to get its guns working again.

When you get inside you see that the building consists of a lot of desks and generally laid out like a bureaucratic office. You briefly think that maybe this was all for nothing and your hunch was wrong, but sure enough when an automated repeated pops up out of the floor and puts several holes into one of Renly's platoon and more golems appear from other trapdoors in the floor you're fairly certain you're still on the right track.

You and Renly's ever dwindling platoon take care of your assailants though at this point they're probably hoping there aren't too many more.

"Glad this building doesn't have multiple floors." One soldier remarks.
"It still might, those golems came out of the floor. There might be several basement levels." Renly points out.
"It can't go too far down, the city is flying in the air now. It's not going to be a Derro complex." You say peering door one of the trapdoors.
"Derro?" Renly asks.
"Oh. Before your time I suppose. They were a subterranean race that were primarily hostile isolationists and had a knack for technology. Sort of like the current gnomes I suppose. I always wondered if they were related in some way to be honest." You answer.
"And they were enemies?"
"Allies actually. Well… such as they were. Anyway I imagine whatever is causing this city to fly would be located right under it, so we might as well start searching there especially since the rest of this building looks more like an oversized office rather than any example of engineering.

You all descend down one of the trap doors and find yourself in some small narrow corridors. Not so small that you can't move around, but certainly small enough that you all have to crouch down. Even at the best of times your body aches, this bending and stooping routine just makes it worse for you. The corridors are also filled with a light steam with gears, pumps and other manner of machinery that you assume are keeping this city afloat. A noisy hum and the occasional jarring metal on metal screeches also surround you and you briefly wonder just how much solid stone floor is between you and the sky right now.

"Guess the gnomes designed this part of the city." Renly says.
"Never thought I'd say this, but I wish we were kobolds right about now." Another soldier remarks.
"Alright let's focus. The good thing about this corridor is I can easily shield us from any attack from the front or the back but you're all going to have to fire upon on any enemy that attacks us. If I start throwing magic bolts or whatever around here I'm libel to damage something severely and send this thing crashing to the ground with us in it.

You travel the corridors for what you believe to be an hour at least. It twists and turns, but you remain convinced that SOMEWHERE down here is a control room. In the meantime more gnomes attempt to stop you and while they have better maneuverability your shield continues to protect everyone and you fend off attacks.

"At least they're just sticking with guns now." One of the soldiers says.
"They don't really have choice, explosives or those flame weapons would damage all these gears that are involved in holding up the place." Renly remarks.

While your followers make minor comments about the situation, you begin to notice a slight change in surroundings. The mist that fills the corridors is dissipating, the floors have become steel and now there are actual walls coving the previously exposed engineering. It suddenly occurs to you that the gnomes hadn't actually finished this place up yet and you are now seeing the areas that took priority.

"We're near the control room." You say.
"We are?" Renly says.
"I'm sure of it."
"Wouldn't there be more defenses?"
"I said I think we're near it, we're not actually there yet. For all we know the actual control room has shit we've never seen before." You answer.

"Oh it does, Eternal. It does. Come on in and see." You hear a voice say nearby. You and the others look around and at each other.

"Just continue a little bit forward and turn the corner. Don't worry, you've killed all of my people, but then you always were an expert at such things weren't you?" the voice says.

When you follow the voice you enter a room filled with a bunch of technical equipment and machines. You no idea what any of it does, but its certainly a technological feat that you've only seen matched by Marik when he was growing tank babies.

Also in the room a single gnome sitting in a chair dressed in the traditional leather uniform you've seen others of his kind wearing. He also sports the same bushy facial hair and red cap they all seem to favor. The only main thing that causes him to stand out is that he's obviously older than the ones you've been fighting and he's wearing explosives around his waist with a wire attached to another device he's gripping tightly in his hand.

The other thing that stands out is that he is completely unconcerned about you or your soldiers pointing their weapons at him.

"You know, this really was one of our greatest works. (Sigh) It's going to be a shame to destroy it, but anything is better than letting it fall into your hands. Can't let a gnome killer like you have it can we?" the gnome remarks.
"You speak as if you know me and I don't mean by my present reputation. You speak as if you know me from the past." You say.
"Oh not personally, but my family's ancestors told me stories about you. Yeah, great ancestor Klemto made sure the story got passed down so that something like Gnome's Home could never happen again. One of the few gnomes you didn't manage to round up and have systematically slaughtered."
"Well I see your mind is made up, no point in debating the issue." You answer.
"Oh no, please I'd LOVE to hear your defense on the matter. I could use a good laugh before I blow us all up."

At this point having one of your soldiers shoot him would be counter productive, he'd just release the switch when he died. Rushing the gnome would likely have the same result

Your only option is to cast a freeze spell and encase his hand in a solid block of ice. The problem with that right now is you're exhausted. You'd have to stall for a little time so you could muster up the energy to do it right now.

So you stall for time and engage the gnome in conversation.

"I was just following orders." You say.
"Really now? That's your defense?" the gnome asks.
"It's not a defense because I don't think I have anything to defend against. The Emperor…Casimir hated your kind. Not I. Why he hated your people so intensely I cannot say because I never fully understood the depths of it. He gave reasons, but as I said I believe there was more to it. It doesn't matter though, since I merely acted on his orders."
"So you were just a blindly loyal soldier just doing your duty eh?"
"At the time yes. Look, if you want me to beg for my life, you'll not get it here. I didn't begin my life as an Eternal begging so I'm certainly not going to end my life begging."

"I see…I suppose I should've known your arrogance and lack of emotions would prevent you from such actions…" the gnome remarks, but you cut him off.
"Funny you should say that. Since I would think someone with the same arrogance and lack of emotions would understand." You say.
"What?!"
"THIS! This flying fortress! And all your airships! You really expect me to believe you designed them for peaceful purposes?"
"We had to protect ourselves!"
"Against the Xi, yes I can see that, but you've been bombing us as well and we didn't even declare war on you!"
"Bah! You would have eventually! And your pathetic attempt at comparing us bombing your soldiers and you rounding up gnome civilians for slaughter is laughable."
"I wasn't actually, I'd say that would be closer to what you did to the original citizens of this city. So what did you do with Telis' original citizens?"

The gnome begins to get annoyed.

"Nothing. This city was always ours!"
"Bullshit. Maybe this place was wrapped in mystery, but not to such a degree that it wasn't known that humans lived here. Or at least they USED to live here. Just looking at the buildings and one can tell that this place was originally designed for humans rather than the smaller architecture that make up these corridors. So how did you go about it? I'm actually curious how you managed to wipe out an entire city without anyone getting a hint of what was going on. I know from your reputation that you don't associate with other races any longer so I can only assume that you had the citizens of this city done away with long before you actually moved in and started making this place into a flying city. Perhaps maybe like something similar that was done to the gnomes?"

The gnome now actually gets off his chair and both of his hands are balled up in anger, which is good since you want him to grip that kill switch as tight as possible.

"It was a completely different situation!" the gnome exclaims.
"Was it? Your ancestor said we rounded gnomes up to be slaughtered, what he probably didn't know since he avoided capture is HOW we did it. We didn't just kill them. We completely obliterated their souls. It's what the Emperor wanted. Then again, you lot probably didn't go that far…no magical skill to speak of, I guess that's why you like your mechanical toys so much…"
"You're going to pay for your crimes you evil bastard. When I release this switch my only regret is going to be that you won't suffer!"
"No doubt. But it's a shame that the real culprit won't taste your justice after you blow us all up."
"What're you talking about?"
"I'm talking about the main executioner. Maybe I rounded some up and killed a few and the Emperor gave the orders, but there was one in particular who was enjoying the job around the clock. She's still alive too you know, or maybe you didn't. She isn't very mobile or social these days. All I'll say is she's a svelk and she's the mother of that bitch that currently runs Lenay, well assuming Lenay hasn't been overrun by the Xi…"
"ENOUGH! This ends now!" the gnome yells getting ready to release the switch.

"Truer words have never been spoken." You say and cast a blast of frost at the gnome's left hand and fortunately you encase his whole arm in ice before he can release his hand from the switch. You collapse on the floor just from that small feat of magic. You really need to rest.

The gnome desperately tries to break the ice, but the remaining two soldiers from the platoon restrain and knock him out.

"Take this little shit topside and throw him off the city. Renly and I will try to figure out the controls to this thing. And do it quickly, that arm won't stay frozen and there still might be some gnomes running around." You say and drag yourself to sit up against a nearby wall.

"Emperor are you okay?!" Renly asks.
"I'm fine. Just very very tired. And unfortunately my work isn't even done yet…" you answer.

"But just maybe this thing will make it easier at least."

You mysteries revealed (Notes on Telis and Gnome Plans)

After successfully bringing Telis under control and eliminating the gnomes still in the city and either driving off or destroying the nearby airships, several notes, books and journals are found and it's a veritable treasure trove of information solving more than a few mysteries and indeed confirming some of your own suspicions.

Telis was mostly inhabited by humans (and perhaps a few elves) and it's technological bent was due to its proximity to Marik's old factory. Apparently during the initial days of the Cataclysm, many managed to take refuge in the place and the survivors in time founded Telis.

One of the journals is extremely old, nearly destroyed and barely legible, but you manage to make out that the writing is derro on the few pages it has left. And to your surprise its must be Marik's. There's no name, but the type of language used and some of the references signify that it could only be him.

One of the more… coherent entries catches your attention.

Entry 101

Fuck! Fuck! Fuck! Fuck! Fuck! Fuck! I do everything around here and those ignorant fucking surfacers appreciate nothing! I don't need this shit! I'm a fucking shit king! I mean I'm king of shit! I don't have to play third fiddle to some fucking eternal and his svelk bitch! I'M the damn fucker! The KING OF THE FUCKERS!

I need to remember to eat today.

Who the fuck does he think he is telling me my creations are no match for him? Fuck him! Fuck him with a fucking horse dick! Dick! Dick! DICK! I know what I'll do! I'll slaughter them all! Drown 'em in their tanks! That'll teach them for failing me! And then I'm leaving this shithole and then the Emperor will see his lack of vision for listening to his idiotic so called son! FUCK THAT SVELK FUCKER!

Perhaps I should work on dirt golems. Why not? There are stone ones and iron ones. Why not dirt? There's a bunch of dirt! I could create a fuckload of them! And then I could be a FUCKING MASTER!

Must remember to take this journal with me. This is good stuff.

The remaining pages contain a lot of drawings of schematics and similar things that you guess went through Marik's insane mind, but nothing more about the "tank babies" who you assume Marik had killed like he mentions he would.

You can only assume Marik himself must've died during the initial chaos of the Cataclysm due to the fact that his journal was found by the survivors hiding out there. Probably killed during the violent earthquakes and shockwaves that caused cave-ins and tunnel collapses.

Getting back to Telis, the place managed to maintain a better standing due to not falling into the dark ages so easily and by staying closely guarded. When the svelk founded Lenay, Telis became even more unwelcoming to strangers and effectively closed its doors too all.

Or at least it did until the gnomes founded the Redcap Kingdom.

Despite the gnome's new outlook on life they noticed that due to Telis being the only other closed society that embraced technology they secretly made contact with them. Telis was suspicious at first, but due to similarities, in time the rulers of the city became more open to the idea of trade and even visits.

It would be a grave mistake on their part. The population of Telis was indeed annihilated by the gnomes, though apparently it was an insidious process. Worthy of a svelk actually.

They slowly and gradually poisoned the water supply. Not to a degree that people were dying instantly either. Just to a point where apparently they couldn't reproduce anymore and in many cases a lowering of intelligence as well. Over the decades, eventually when the population was low enough, the gnomes offered "help" and then proceeded to exterminate the rest in a more traditional fashion. From there, they worked on turning the entire city into a flying fortress. You wonder why they just didn't do this with one of their own cities, but if you had to guess, their own cities were under constant attack by the Xi (especially underground) making ongoing work problematic (Hence their hasty attempt to get this one up and running when the Xi started becoming more of a problem in Arat)

From what you can tell this all started before you were even dug up. At least according to Flemto Zookwinkle's journal here. (What a silly name) You're guessing he's the one that confronted you and is now nothing more than a bloody red spot on the ground.

You've found some other plans and scraps of info about what the gnomes were up to recently as well, but a lot of it is pretty technical and some of it looks biological. Specifically Xi. Maybe they were looking to poison the Xi somehow too.

In any event, you decide to let your inventors and doctors take a closer look at the mess and maybe they can figure out how to apply it.