Especially a bath that has nothing to do with getting clean. In Budapest, baths are for healing, playing chess, socializing and relaxing. The city sits over what seems like an infinite number of natural hot springs. For over 1000 years, people, right back to the Celts, have been raving about how wonderful they are. But it was the Ottomans who really amped up the spa experience, building huge palace-esque places for plunging from pool to pool.
Amazingly, many of these from the 16thand 17thcentury still exist. Among the best known are Rudas (Turkish dome and octagonal pool), Kiraly (very old, very traditional) and Csaszar (well restored, a bit more state of the art). Play sultan, or sultana, and soak in their therapeutic waters.
Baths built at the turn of the last century are wonderfully decorative and ornate; just screaming for ostrich feathers and bustle dresses. Gellert is oh so art nouveau; Lukacs features an exterior wall covered in historic thank you tablets left by grateful, cured customers dating back to 1898; Szechenyi is huge, central, the best place for chess and a personal favorite.
Visiting is a bit of an adventure. All are geared for local people so can be a bit intimidating for tourists; there is not always a ton of English. Best to bring your own suit, bathing cap (ick, but required in most pools), water bottle and towel, though rentals are available. Depending on which Bath you visit it may only be open to a single sex at any given time, check in advance.
When possible, get a private cabin for changing and leaving your stuff. There are no rules as to which pool in which order. Following a local is a good place to start, and then just move as you feel the need either for cooler or hotter water. Massages, mani-pedis and a wide selection of treatments can be booked too. Who know if the water actually heals anything? I do know I always feel better after.