Belief in the curative powers of Tarapaya (3600m), the most frequently visited hot-springs area around Potosí (21km northwest of the city), dates back to Inca times. It even served as the holiday destination for Inca Huayna Capac, who would come all the way from Cuzco (now in Peru) to bathe. The most interesting sight is the 30°C Ojo del Inca, a perfectly round, green lake in a low volcanic crater, 100m in diameter.
Along the river below the crater are several very developed balnearios (resorts) with medicinal thermal pools (B$10) utilizing water from the lake, but best to stay close to the edge since remolinos (whirlpools) make bathing here a hazardous affair.
Camiones leave for Tarapaya (B$4, 30 minutes) from Mercado Chuquimia near the old bus terminal in Potosí on Av Antofagasta roughly every half hour from 6am to 7pm. Taxis cost about B$70 one way. The last micro from Tarapaya back to Potosí leaves between 5pm and 6pm.