Visit the Turda Salt Mine

Underground cathedral carved into the tunnels of a working salt mine.

Snorkel over WWII bulldozers and trucks the US Army dumped into the sea.

Sunken Byzantine reservoir under Istanbul, its columns rising from black water.

Ride one of the world's longest trains.

Jagged coral pinnacles of the interior.

Explore the historic silver mine in Tarnowskie Gory, a UNESCO World Heritage site with underground tunnels and mining history

Visit the Krzemionki prehistoric flint mines in Poland, a UNESCO World Heritage site showcasing ancient mining techniques and Neolithic history

Silver-mining city of candy-coloured houses stacked up a ravine, with streets in tunnels and student minstrels serenading the alleys.