Rudas Thermal Bath

Rudas has been a working bathhouse since the Ottoman occupation of Buda in the 16th century, and the octagonal central pool — lit by pinpricks of daylight through a star-perforated dome — is the original structure, not a later reconstruction built to look old.

It runs a mixed schedule now, though for most of its history the bath kept to men-only hours on most days; check the current timetable before planning around it, since Rudas is one of the few Budapest baths where the historic core and the modern wellness extension (a rooftop pool with a river view) sit side by side rather than one replacing the other.

Go for the Ottoman pool itself rather than the newer additions — that's the part nothing else in the city replicates.