Mixed gender, clothing optional spa in Chicago area?

Does anyone know of a spa with sauna, whirlpool and similar services that (a) doesn't require clothing and (b) permits my wife and I to spend time (relaxation, not sexytime) together?
Most facilities are gender separated, especially if clotheslessness is involved.  King Spa in Niles actually requires clothing (supplied) in the mixed sauna areas, and is gender separated in the pool areas which is very annoying.