Lake Proval, Underground karst lake at Mount Mashuk, Pyatigorsk, Russia
Lake Proval is an underground karst lake in a cave formation at Mount Mashuk in Pyatigorsk, Russia. The mineral water reaches about 11 meters deep and extends across a diameter of roughly 15 meters.
Professor A. P. Nelyubin conducted the first detailed chemical analysis of the lake water in 1823 and measured its dimensions during his summer research. The horizontal tunnel to the lake was constructed in 1857 and allowed direct access to the cave.
Bronze lion sculptures guard the entrance, and a statue of the fictional character Ostap Bender recalls his invented scheme to sell tickets. Visitors often notice the turquoise tint of the water, caused by its high sulfur content, which gives the place its distinctive appearance.
The lake can be reached through a horizontal tunnel that runs inside the mountain and is walkable for visitors. Lighting inside the tunnel helps with orientation, and the path ends at a viewing platform above the water.
The water temperature ranges between 26 and 42 degrees Celsius, giving the lake a warm feel even when the outside air is cool. The high hydrogen sulfide content not only gives the water its color but also a slight smell that is immediately noticeable.
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