This is a solid affordable option right in the castle district. Clean plus beautiful architecture.
Pros: 1) Location! If you want to get up early or stay up late and avoid all tourist rushes around the castle and Charles bridge, this spot can't be beat - it's a few blocks away from both. 2) Host was great at communicating. 3) Between the gorgeous hardwood floors and vaulted ceilings, it "feels Czech" and could be the backdrop to some great pics. 4) The street was very quiet all night even though it's on a main street as far as tourism goes. 5) Building is secure. There were 4 locks between the apartment and outside. Felt very safe as a solo woman traveler.
Cons/ extra info: 1) I would not recommend this to anyone with mobility difficulties. It's located on a steep hill and there are no elevators in the building. 2) The bathtub had a Czech style shower that is mounted low for sitting in the tub, not at all ideal for stand up showering most western countries are used to. This can be awkward/ dangerous if you aren't super flexible. The water heater is fairly small so if you are 2+ people who need to shower every day, I could see someone ending up with a cold bath. 3) Would have liked more than 1 bath towel, but not a big deal. 4) Kitchen is fairly bare bones. No dishwasher. They have a drip coffee maker. A Nespresso Machine would be nice so that you could bring your own coffee without having to take up a lot of luggage space, and they are faster than waiting for a pot to brew. I didn't notice a can opener in case you need one. 5) No air conditioning. Get used to (beautiful/historic) open windows (without screens). This is very common in Prague so I hesitate to add it as a con - but if you are expecting air, it's not there. They have fans. If you keep the shutters closed in the day, the apartment will stay much cooler.
Tip: Use the trams for travel too! They will save you a lot of time and energy over walking all the way to the metro stops. You may need your energy to get back up the hill :)