Medusa Head, Byzantine Basilica Cistern, Sunken or Underground Palace, Sultanahmet, Istanbul, Turkey, Europe

Tourist exploring the underground halls at Diocletian's Palace, UNESCO World Heritage Site, Split, Dalmatian Coast, Croatia, Europe

Underground halls, Diocletian's Palace, UNESCO World Heritage Site, Split, Dalmatian Coast, Croatia, Europe

Old ruins and colonnade of the underground Minoan Palace of Knossos, Heraklion, Crete, Greek Islands, Greece, Europe

Water reflecting columns at Basilica Cistern (Sunken Palace) subterranean water system underground, Istanbul, Turkey, Europe

Tourists exploring the underground halls at Diocletian's Palace, UNESCO World Heritage Site, Split, Croatia, Europe

Paradise Garden with Garden Grotto, Neuburg am Inn Castle, Neuburg am Inn, Lower Bavaria, Bavaria, Germany, Europe

Light installation in the Roman vaults in the cryptoporticus under the Diocletian Palace in Split, Croatia, Europe

Light installation in the Roman vaults in the cryptoporticus under the Diocletian Palace in Split, Croatia, Europe