Hévíz is one of the world's great natural wonders — the largest biologically active natural thermal lake on earth, covering 4.4 hectares near Lake Balaton in western Hungary. The lake's spring, 38 metres below the surface, pumps 80 million litres of water every day at 38–41°C, keeping the surface temperature at 23–25°C in winter and 32–34°C in summer. The lake can be bathed in year-round. The sulphurous, slightly radioactive mineral water is medically proven to benefit arthritis, locomotor disorders, inflammatory diseases, and post-operative recovery. The lake is surrounded by a covered bathing pavilion with wooden walkways, changing cabins, and a central spa and therapy centre. The town of Hévíz itself has numerous hotels offering thermal treatment packages.