Not a natural cave but a labyrinth: for centuries people quarried marl (soft limestone) out of the hill at Maastricht, leaving over twenty thousand passages under the Dutch-Belgian border, walls covered in charcoal drawings and signatures going back to the 1500s. It sheltered people in both world wars, and Rembrandt’s Night Watch was hidden here from the Nazis. Guides only, and for good reason: people have died lost in it. PUBLIC guided tours, Maastricht, Netherlands.
Netherlands
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