A narrow tunnel running around the perimeter of Pampus, an artificial island and late 19th-century sea fort in the IJmeer near Amsterdam.
The island fort was once part of the Defence Line of Amsterdam – a 135km long system of fortifications that defended the city, and were capable of flooding large portions of the Dutch countryside to deter invaders.
Visiting the abandoned fort is an easy trip from Amsterdam, and there are lots of interesting things to see and do when you get there.
But my favourite part of Pampus is this shadowy tunnel that runs around the perimeter of the fort.
I especially enjoyed the sections where the lights stop, and you need to use a flashlight to find your way.