Good point, Alawyer. If memory serves (I was there last November) this one opens at noon on weekdays, but runs 24hrs on weekends. Best to check their website, which oddly enough I can't seem to locate anymore...

If closed in the morning, MikeKN can take a walk on Zeil street with its shops and eateries, and walk along the river. I still recommend even a quick stop at the sauna: a shower and a soak in a hot tub between two long flights is really a blessing.