Beneath the baroque façades of Prague's Old Town lies a labyrinth excavated nine metres below the Vltava's historic flood line, where Romanesque foundations and Gothic cellars have survived eight centuries of sieges, fires, and royal decrees. The city built upward after catastrophic flooding in the 13th and 14th centuries, sealing entire ground floors beneath new cobblestone layers. What remained below became storage vaults, torture chambers, and eventually smugglers' corridors. The dungeon complex beneath Malé náměstí, a medieval square northeast of the Astronomical Clock, preserves interrogation rooms used during Hussite Wars trials and iron cages anchored to limestone walls. Guides recount the 1621 execution of 27 Bohemian nobles in Old Town Square, whose restless apparitions reportedly drift through underground passages on winter solstices. The Prague Ghosts Legends Medieval Underground & Dungeon Tour grants access to these subterranean chambers, where costumed interpreters recount plague-era burials and alchemist experiments conducted under Rudolf II's patronage. The medieval cellars extend beneath five interconnected buildings, forming a network that once linked merchant houses to the river quay. Археological surveys in 1997 uncovered Romanesque stonework predating Charles Bridge, along with Renaissance graffiti etched by imprisoned heretics. The dungeon's iron maiden replica and stretching rack occupy a vaulted chamber that served as a municipal jail until 1784, when Joseph II's reforms abolished judicial torture. Humidity levels remain constant at 12 degrees Celsius year-round, preserving original timber beams blackened by tallow lamps. Prague's underground tours illuminate the city's vertical history, where street level rose in increments measured by catastrophe. The Gothic cellars beneath Týn Church, accessible via separate archaeological routes, reveal how merchant guilds expanded downward when lateral growth became impossible within fortified walls. These subterranean spaces served functional roles—wine storage benefited from stable temperatures, while hidden chapels sheltered Protestant congregations during Counter-Reformation crackdowns. The dungeon tour emphasizes spectacle over scholarship, but its corridors occupy genuine medieval infrastructure. Visitors descending the stone staircase at Malé náměstí enter chambers where interrogators once kept meticulous Latin records of confessions extracted under duress, ledgers now archived in the National Museum's manuscript collection.