Hello, I speak from experience, so this won't be as informative as more experienced players would put it...
Cruising Bars :
Being very few of them in Taipei, the only one I know of with a cruising area is Commander D 司令, this is more of a fetish club.
Sauna:
Saunas are more popular in Taipei. Those are the saunas I know :
ANIKI : Used to be (still is?) the crown jewel of Taipei gay sauna. fit and young mostly, very new establishment, all kinds of events. Have their own web page if you are interested.
Hans Men's Sauna 漢士三溫暖 : this one is for mixed age and shape, old establishment bur well maintained, very crowded even in mid-weekdays.
Soi 13 in : this one is pretty new, the facility it self is huge, not been there often, more for slim shape ones.
I/O Taipei Sauna : this one is also new, bears mostly, have special events during weekend evening.
XL Club : old establishment, very small space, more of a fitness training studio with a bar and wet sauna room attached to it.
Palace 皇宮 : very old establishment. Probably one of the oldest ones still exist, elders mostly.
Grand Shanghai Sauna 大上海三溫暖 : don't really have an English name, it's translation only. locate inside of a traditional market. mixed age and shape.
That is all the info I could put together for now, feel free to message or post if you have any questions.