Beneath Malé náměstí and the surrounding streets of Prague's Old Town lies a network of Romanesque cellars, Gothic crypts, and Renaissance storage vaults that predate the square itself by three centuries. The oldest passages descend to foundations laid in the 11th century, when merchant houses built their ground floors at the original medieval street level—today nine metres below the modern pavement. Periodic flooding from the Vltava forced successive generations to raise the city, entombing entire ground floors and turning wine cellars into multi-level labyrinths. By the 14th century, these subterranean corridors served as trade routes, smuggling passages, and improvised dungeons during the Hussite Wars. The Prague medieval underground and dungeon tour opens access to chambers that municipal authorities sealed for five centuries. Torture instruments displayed in the deepest vaults—iron maidens, thumbscrews, and heretic's forks—are reproductions based on Bohemian judicial records from the reign of Charles IV, though the stone interrogation cells and rusted shackles mounted in limestone walls are original. Guides interpret faded inscriptions scratched by prisoners awaiting trial under the medieval legal code, which permitted judicial torture until Maria Theresa's reforms in 1776. The Gothic hall beneath the Old Town Hall retains its ribbed vaulting and original flagstones, worn concave by six centuries of foot traffic before the space was abandoned in 1784. Today the underground tours reveal not only criminal history but also the architectural evolution of a city rebuilt layer by layer. Visitors descend through Romanesque barrel vaults into Gothic pointed arches, then emerge through Baroque passageways that connect medieval basements to 18th-century utility tunnels. The temperature holds steady at 14°C year-round, and the humidity preserves timbers and masonry that would have rotted at street level. Chalk marks on the ceilings trace the routes of 19th-century surveyors mapping the labyrinth for the first time since the Thirty Years' War. The dungeon chambers lie directly beneath the Astronomical Clock, and acoustics carry the hourly chime through limestone walls into the deepest interrogation cells. Guided underground experiences operate daily from Malé náměstí 459/11, with tours departing on fixed schedules between 10:00 and 18:00. The standard route covers 400 metres of passages and descends 12 metres below street level, requiring 90 minutes and moderate fitness. Specialists in medieval Bohemian history lead the dungeon-focused variants, which include extended time in the torture exhibit and access to sealed sections normally closed to the public. All tours conclude at street level within the Old Town perimeter.