Budapest sits on a geological fault, and along it more than a hundred thermal springs come up through the limestone. The Romans built on them at Aquincum. The Ottomans, who held Buda from 1541 to 1686, built domed bathhouses that are still operating. The Habsburg and Dual Monarchy periods added the palaces. No other capital in Europe has anything like it, and using the baths is not a tourist activity here — it is what people do on a Tuesday.
The four you might choose between
Széchenyi, in the City Park, is the largest medicinal bath complex in Europe: eighteen pools, three of them outdoors in a yellow neo-Baroque courtyard. The outdoor pools are the famous ones, with the chess players and, in winter, the steam. It is busy, social and slightly chaotic. If you go to one bath, this is probably it.
Gellért, attached to the hotel at the foot of Gellért Hill, is the beautiful one: Zsolnay ceramic, a vaulted glass roof, marble columns, an Art Nouveau scheme of 1918. Smaller, calmer and more decorative. Come here for the architecture.
Rudas is genuinely Ottoman — a sixteenth-century octagonal pool under a dome pierced with coloured glass, which throws discs of light onto the water. It has traditionally run single-sex days and mixed days; check the current schedule before you turn up, because it changes. There is also a modern rooftop pool with a view over the river, which is a strange and excellent combination.
Király, also sixteenth-century Ottoman and smaller still, is the least developed and the most atmospheric of the old ones.
What to bring
A swimming costume — required everywhere in mixed sections. Flip-flops, which matter more than people expect on wet stone. A towel. A swimming cap if you intend to use a lap pool, where it is compulsory.
All of these can be hired inside, at a markup, and the hire queue is often longer than the entrance queue. Bring your own.
Locker or cabin
Every bath sells entry with either a locker or a cabin. A cabin is a private changing cubicle and costs a little more. Take the cabin. Lockers mean changing in a shared area and juggling a wristband, and the difference in price is small.
The wristband is your key: you press it against the locker or cabin door to lock and unlock. At some baths you are assigned a number at the desk; at others you choose your own and the band remembers it.
The unwritten rules
Shower before entering a pool. Do not swim lengths in a thermal pool — they are for sitting in, and people will look at you. Keep to short sittings in the hottest pools, twenty minutes at most, and cool down in between; the 38 to 40°C pools are medicinal rather than recreational and they will make you light-headed if you treat them like a hot tub.
Drink water. Do not go in having drunk alcohol.
Photography is restricted or forbidden in most indoor sections. Nobody minds a phone by the outdoor pools at Széchenyi; everybody minds it in the Ottoman domes.
Timing
Early morning, from opening, is the quietest hour of the day at every bath in the city by a wide margin. Weekend afternoons are the busiest. If you have any flexibility, use it.
Winter is better than summer. The outdoor pools at Széchenyi in January, with snow on the balustrades and steam standing in the air, are one of the great experiences in Central Europe. In August they are simply a warm swimming pool with a queue.
What it costs and what it is for
Entry to the major baths is not cheap by Budapest standards but is modest by Western European ones, and it buys you several hours. Massages and treatments are booked separately and are worth arranging in advance in season.
Hungarian medicine takes the waters seriously — they are prescribed for rheumatic and joint conditions, and a proportion of the people around you at nine in the morning on a weekday are there on a doctor’s recommendation, not a holiday. That is worth knowing, because it explains the atmosphere. It is a public facility that happens to be beautiful, not an attraction that happens to have water in it.
What to avoid
The night-time “sparty” events held at Széchenyi on some Saturdays are a nightclub in a swimming pool and bear no relation to the daytime experience. If the baths are what you want, do not book one of those by mistake.