Gremyachy Waterfall, Natural waterfall in Sergiyevo-Posadsky District, Russia

Gremyachy Waterfall is a cascade in Moscow Region where water from the Gremyachka flows over a rocky ledge. The water runs down in several narrow streams and collects in a small pool at the base of the cliff.

The spring is linked by legend to the prayer of Sergius of Radonezh, who is said to have caused the waterfall to appear. The site is now a metochion of the Trinity Lavra of St. Sergius, with a church, a chapel and a bathing pool built around it. It holds the status of a regional cultural heritage site in Russia.

The name Gremyachy comes from the Russian word for thunder, reflecting the sound of falling water. Visitors come here to drink fresh spring water believed to be especially pure.

Access requires a walk of roughly half an hour through wooded terrain with uneven paths. The area is best visited in dry weather, as paths can become slippery after rain.

The springs emerge from fissures in limestone about halfway up the steep Voндига slope, and the water is enriched with radon, a colourless radioactive gas; bathers fill the fonts beside the falls. The name Gremyachy meant "noisy" to the Slavs, who gave it to springs they believed had broken out where lightning struck.