There are also luxury hotels that do not permit outsiders to use their spa. Raffles in Singapore is an example.

Many spas have combination or all day packages, sometimes for couples too, that include a light lunch as well as usee of pool, sauna, etc. facilities.

Personally, I think of spas as primarily pseudo medical emphasis (most of the spaas in Germany, which may have qualified medical doctors on staff), primarily cosmetic (waxing, manicure/pedicure, facials, etc., often in free standing locations), and primarily relaxation (antistress and anti-jet lag massages, often in luxury hotels)