Bad Gastein's most striking sight costs nothing: the Gasteiner Ache waterfall splits the town in two, dropping 85 metres in three cascades right through the centre. Everything else radiates from it. The Felsentherme thermal baths are carved into the cliff next to the falls and are the reason most people come. The 19th-century grand hotels on the upper town are worth a stroll for the architecture alone, even if most are now apartments or hotels again — look up at the Straubinger, the Kaiserhof, and the decaying Badeschloss for a sense of the place's former ambitions.
For outdoor activity, the surrounding mountains offer well-marked hiking trails in summer and access to the Ski Amade region in winter.