Barcelona has an incredible number of spas ranging from high end to more moderate. Most of the fancy spas are found in the city's large number of hotels with the Arts, W and Majestic housing some of the more popular ones. Treatments are usually pricey at the hotels, but the gorgeous panoramic city views and impeccable service makes it worthwhile. Most of Barcelona's spas offer an 'East meets West' fusion of treatments with professionals who specialize in the specific art.
If you've had a long day of touring and just want to kick back and disconnect, most of the spas have special quiet areas where you can listen to music, read or close your eyes and take a nap. They also offer an array of pools including hot tubs, whirlpools, individualized tubs and hot and warm baths. A recent addition to the spa scene is the arrival of the juice bar. Barcelona is getting to be a healthier city (little by little) and many spas have introduced the juice and gastro bar where you can have a fresh fruit or vegetable smoothie accompanied by authentic Spanish tapas (the non-greasy kind).
Even if you only have a short stay in the city, it's worth it to spoil yourself for at least 30 minutes in one of Barcelona's amazing spas.