The three small ponds in an abandoned quarry offer unusually clean water and are popular for sunbathing and swimming.
Note that this is an unofficial bathing spot and the place is partially behind a fence. You will encounter nude bathers on sunny days, clothing is considered optional here.
Wikipedia https://cs.wikipedia.org/wiki/Růženin_lom
Address Růženin lom, Jedovnická, Brno 62800, Czech Republic
Coordinates 49°13'2.515" N 16°40'21.57" E