The thermal baths in the Nagyerdő are the practical reason most Hungarians know Debrecen. Aquaticum draws on a hot spring discovered in 1932 and now feeds an indoor "Mediterranean" pool complex, a more traditional outdoor strand, and separate medicinal pools recommended for rheumatism, joint pain, and post-operative recovery. Locals treat them as a year-round routine; visitors find the indoor pools more interesting on a winter weekday, when the contrast with the cold city outside is the entire point.
Allow at least three hours. Bring flip-flops, a swimming cap (required in some pools), and small change for the lockers. The complex is at the eastern end of the Nagyerdő tram terminus.