Very unstable and slow wifi. If you need some for your job, consider like you don't have it at all.
It often smells moldy and moisture, sometimes from tubes as well.
Gaps in the windows frame, so it's always very noisy and wet. (Note that istanbul is an extra noisy city itself due to the culture specifics).
It also might smell if someone is cooking or smoking inside or outside.
Rusted floor in the shower cabin