Tapolca Lake Cave, Underground cave system in Tapolca, Hungary.

Tapolca Lake Cave opens from a visitor building at 3 Kisfaludy Sándor Street, 132 m above sea level. Its developed section has stairs, walkways and electric lighting; the 340 m tour route includes a boat ride through water-filled passages. The cave forms part of the Tapolca cave system after its connection with the Kórház-barlang.

In 1902, thermal-water caves were found while digging a well at a house on Győri utca, which drew interest from far beyond Tapolca. The name Tapolcai-tavasbarlang first appeared in literature in 1933. Since 1982 the cave has been one of Hungary's specially protected caves, and it was later connected with the Kórház-barlang to form the Tapolcai-barlangrendszer.

The cave has been called Tapolcai-tavasbarlang in written sources since 1933, and older texts also used names such as Tavas-barlang and Tó-barlang. Visitors enter through a building at Kisfaludy Sándor Street 3 and pass halls named after Lóczy and Batsányi, where debris was cleared before tours began.

The cave is entered from the visitor building at Kisfaludy Sándor Street 3, at 132 m above sea level. The 340 m route, partly covered by boat, takes 30 minutes and is equipped with stairs, walkways and electric lighting. The air is 18–20 °C with 100% humidity, so dress accordingly.

The warm karst water keeps the cave air at 18–20 °C with 100% relative humidity. On the walls and along fissures, small 1–2 mm calcite crystals and pine-branch-shaped aragonite clusters grew from aerosols where airflow suddenly changes direction.