As written in the description, it is on the 5th floor and therefore probably not for the elderly or unfit. For everybody else, climbing the stairs is rewarded with the most panoramic views over the Bosporus river (front-side) and Galata mountain (back-side). So even if you want to relax inside for a day, you can still enjoy the full Istanbul experience.
The apartment itself has a nice retro decoration and is equipped with all kinds of "neciccities" – I lived there for a month and didn't lack anything.
Daniel himself is a wonderful host who can provide you with literally all information that you will need. He made my stay extra comfortable and he answered all the questions that I had swiftly. Happy that we had the chance meet in Ankara :)