I used the showers at TK's CIP lounge in IST once. I found them usable, but IMO, describing them as nice is a bit of a stretch. The disposable towels were not great to use (you'll have to ask for more from the front desk before hand because 1 set IMO is nowhere enough). The layout is more like a common shower facilities you find in clubs where there are separate shower cubicles but a common changing/locker area; IIRC, in the case of the IST showers, there are also lockers outside of the (2 I think) shower cubicles.

Adequate but I reckon inferior to the setup in lounges at other airports (BKK, ZRH, SIN etc.) where each separate cubicle comprised at least of a shower area, a wash basin area and space to bring in hand luggage for a proper change, and in many cases, there was even a toilet.