The oldest written record regarding the springs at Sliač can be traced back to 1244, the reign of King Belo IV. Starting in mid-15th century, the Sliač springs are referred to by a number of distinguished scholars and authors such as Aeneas Sylvius, nuncio to the court of king Matheus Corvinus (1458 – 1490) at Buda, the German Georgius Agricola, chief alderman and municipal physician of the city of Banská Štiavnica, Juraj Wernher, “founding father of balneography in the Hungarian Empire”, and many others.

As a spa, Sliač was in operation as early as in the 16th century. Historically it ranked among the Empire’s most popular spas. Its popularity and attraction were attributed to the healing qualities of its mineral waters as well as visits by prominent figures of politics, business and arts (e.g. the Hungarian revolutionary Lajos Kossuth, Austrian playwright Franz Grillparzer, Czech woman author Božena Němcová, Czechoslovakia’s first president Thomas G. Masaryk, Soviet president Khrushchev etc.). The list of famous guests is long and includes, among others, the Cambodian prince Norodom Sihanouk.

By the middle of the 19th century, a two-storey bath-house had been erected, with four baths: Panský (Herrnbad), the one with the highest temperature, Meštiacky (Bűrgernbad), Sedliacky (Bauernbad), and a cold pool, referred to as Ľudový (“folk bath”), with the lowest temperature. All of the baths used natural springs. In addition, two hotels had also been built: Detva and what is today Bratislava. Two privately owned houses that had been adapted to provide accommodation also proved popular. They were Thőkőličkin dom (Madame Thőkőly’s; it was later replaced by the Amalia bathhouse) and Szeréničkin dom (Madame Szereny’s).