The underground of the city is extremely rich in various types of well-cured sour waters and is therefore often referred to as the city of thousands of wine waters. Carbonated mineral water and carbon dioxide eruptions are everywhere. The cellars are full of otherwise life-threatening carbon dioxide, but the natives, using the opportunities of nature, have transformed them into private mofettas.

One of the natural science and tourist attractions of Covasna is the Hell's Square in the town's main square, which is nothing more than a mudslide of sulfur-carbon gas. It used to be a spa, though it still dominated the entire Main Square. Opened in 1881 under the name "Hellbath Spa Institute", Covasna became one of the well-appointed spas. The later spa settlement was established on the Mikes site in Vejnafalvi, called Mikesfürdő.

There are several mineral water springs in the spa town. One of the curiosities is the water of the Pancake Fountain in Vajnafalva, which contains so much sodium carbonate that women knead and raise the stoned pancake.
The waters of the city were already mentioned in 1567, but it was not until 1773 that they were first analyzed. In 1882, the water of the Fisherman's Spring received a gold medal at an exhibition in Trieste. Today, the mineral waters of Kovasna are used only for bathing and not for bottling.

Indications
Drinking water - a medical indication - is served by the water of drilled wells, combined with other treatments, to promote the healing of cardiovascular diseases.