Well-known mineral baths in Bulgaria, ‘Hissarya’, are described. Their existence dates back more than 25 centuries. ‘Hissarya’ is an Arabic word meaning ‘siege of a castle’. Remains of castle walls are the symbol of ‘Hissarya’ today. Every year more than 100,000 patients from Bulgaria and other countries visit ‘Hissarya’. From the time of the Thracians and the Roman Empire until now renal stones have been successfully treated by drinking the mineral water and by taking baths. The Roman Emperor Septimius Severus (193–211) visited ‘Hissarya’ every spring to treat his renal disease.