We had a great stay at Burcin's flat in Besiktas. The flat was comfortable, plenty of space for five people, and had amazing views of the city, along with afternoon sunlight and views of the sunset each evening. There are two twin beds upstairs and two queen beds downstairs in separate bedrooms. All three spaces have their own shower, sink and toilet -- very rare in Istanbul! We enjoyed the comfortable living room (playing cards in the evening), large dining table (simple breakfasts each morning), patio with beautiful views, and the numerous shops and restaurants close by. The Wifi and drinking water provided was very convenient and Burcin was always available by text to answer any questions about the city and the flat. We would definitely stay here again.
Tips: Even though the flat is a bit outside the main tourist area, it's a short walk to Barbaros Blvd and very easy to connect to the bus lines and Metro. To access the upstairs there is a steep set of stairs, for those less agile/well balanced you could climb up and down like you would on a ladder. The ceiling is lower upstairs because the flat is on the uppermost floor and has a pitched roof; a very tall person might find this difficult but kids would probably love it. There is a second balcony upstairs as well. The kitchen is well stocked with dishes and pots and pans etc if you want to have a meal in. There is a washing machine and dishwasher too.