When settlers of Bochnia, Poland discovered a rich vein of rock salt running beneath their town in 1248, it was the medieval equivalent of striking gold. Minerals brought out of the Bochnia mine helped fund the Polish kingdom well into the 16th century, until its prices were undercut by German sea salt.

Today Bochnia is one of the oldest continually used salt mines in Europe, though it has now been given over to another purpose: restoring health. The 950-ft. deep sanatorium, with its own unique micro climate, is thought to help cure respiratory diseases. A 150-meter long chamber with 140 bunk beds is used to house the unwell. The former salt mine also has a chapel carved out of the salt rock, a gymnasium, and a spa. Group jogs through the mine are a commonly organized event.

Visitors to Bochnia needn’t be sick, however. A train whisks tourists about the underground caverns for short tours. Those wishing to stay longer also have the option of detraining for the night as part of an “inhalation stay.” However, you will need to bring friends, as such overnight visits require a minimum of 80 guests.