Only 3 blocks away from Taksim Square (major transportation hub), the location is tucked in an apparently not well known street, as several taxis had difficulty finding it (in spite of it being marked on Google maps - I had to navigate them with my own Google maps). The apartment is on the 2nd floor (Europeans count the ground level as floor 0) of an old building. After climbing a narrow a staircase (about 30 steps), the apt itself is remodeled. It sits on 2 floors with an inner narrow staircase. Off the entryway are 2 spacious bedrooms with a queen size bed each, a living room, a tiny (1 person) kitchen reasonably well equipped (no microwave, no pot, -only a pan for cooking), 1 bathroom with shower. On the upper floor is a bedroom with a single twin-size bed, and a roll-away cot, a bathroom (no shower), and a dining room which we did not use.
The neighborhood has supermarkets, many places to eat. On Taksim square (5 mins walk) are many taxis, a metro/underground that connects Taksim Square to Kabatas, where the T1 tram line starts, that goes to Sultanahmed where all the main monuments are. It's the quickest way to get there instead of taxi due to traffic (and much cheaper). Also a couple of blocks away from Taksim Square is the stop of the HavaIST (the shuttle bus from the new IST airport (which just replaced the old Ataturk airport)) or HavaBUS (the shuttle bus from the SAW airport). It is the best way to come from/to the airport even with luggage, if you are able to walk a few blocks with your luggage. I found out the hard way that taxis refuse to give rides for short distances (even when it rained and I didn't want to walk with luggage), so don't plan on getting a ride from the shuttle stop to this apt.
The apt itself is well equipped, but we had to ask lots of questions on WhatsApp (which Nursena replied to immediately - thank you!) on how to turn on the hot water, how to operate the TV (local programming in a different languages, interesting to learn about local issues). It would be helpful to have a binder with all this info (or post them online) including the metro/tram/local restaurant recommendations/etc.
All in all, I would have preferred to stay in Sultanahmed area as we found ourselves going back and forth there every day. If you want nightlife, then Taksim Square area is probably better.