The Brno Water Tanks are a surprise under Žlutý kopec: three huge underground reservoirs built to store the city's water in the 19th and early 20th centuries. Brick vaults, concrete chambers, and rows of pillars create spaces that feel part cathedral, part abandoned engineering work.
Tours make the most of the atmosphere without turning the place into a gimmick. It is one of Brno's better recent openings, especially if you like industrial architecture or want something stranger than the standard castle-and-square circuit. Book ahead when visitor numbers are limited.