• Tickets online only, with no sales at the meeting point, and advance tickets can't be refunded or exchanged
• Sturdy closed shoes are required (no sandals or flip-flops), and warm layers help underground
• No toilets on the tours, so use the public one at Gesundbrunnen station first; lockers there take bags bigger than a small backpack

Berliner Unterwelten leads guided walks through bunkers and tunnels beneath the city. The Dark Worlds tour starts behind a green door in Gesundbrunnen station and winds through a WWII air-raid shelter left as it was, full of wartime artifacts buried for decades.

Other tours visit a Cold War nuclear bunker and escape tunnels under the Berlin Wall. Talks are pitched at adults, which suits curious teens best.