Badgastein, town in the Gastein Valley of west-central Austria, on the Gasteiner Ache (river). Its radioactive thermal springs have been visited since the 13th century, and royal and other eminent patrons brought it world renown in the 19th century. Now one of Austria’s most important spas and health resorts, it is also known as an international winter-sports centre and is the site of two magnificent waterfalls with drops of 207 feet (63 metres) and 280 feet (85 metres). The town was the site of the Convention of Gastein, under which (1865) Austria gained control of Holstein and Prussia began administering Schleswig. Pop. (2001) 5,838.