Mondorf-les-Bains (French pronunciation: [mɔ̃dɔʁf le bɛ̃]; Luxembourgish: Munneref [ˈmunəʀəf]; German: Bad Mondorf [baːt ˈmoːndɔʁf]) is a commune and town in south-eastern Luxembourg.

Karl Gotthelf Kind, who had found salt in Germany and hoped to do the same in Mondorf, discovered the waters after drilling to a record depth of 736 metres.

Despite their mineral properties, the waters were not suitable for salt a brownish colour caused by the rich iron content which emerged after distilling.

Nevertheless, the local notary, J.-P. Ledure, saw other opportunities for the waters and was successful in finding support for setting up the "Société des Bains de Mondorf".

As a result of the spa's success, the village prospered as rich French guests came to stay in the luxurious hotels which sprang up in the vicinity.

In the early 20th century, the State invested heavily in the resort adding a pavilion for the original source, a banqueting hall and a reading room as well as the Orangerie and the country's first indoor swimming pool.

[4] The spa continued to prosper in the second half of the 20th century with an outdoor swimming pool (1953), a new thermal centre (1988), and the Casino 2000 which opened in 1983.

The organ on the balcony with musical emblems, the confessionals and the altars blend harmoniously with the frescos designed by Jean-Georges Weiser from Bohemia.