The Theta group chose their hiding place well. Bryggen's medieval wooden buildings are a labyrinth of sealed doors, dead-end corridors, and rooms that lead nowhere -- a consequence of centuries of modification, fire damage, and rebuilding. By the time of the German occupation, most doors in Bryggen's buildings had been closed off and sealed. One more sealed door attracted no attention. The young members of the Theta group used their engineering training to design a special electrical locking system that concealed the entrance entirely. Behind that door, in a room measuring roughly four by four meters, they set up their transmitter and went to work sending coded messages across the North Sea to British intelligence.

On October 17, 1942, German forces conducted a raid at Bryggen. The hidden room was discovered by accident: a soldier on the floor above stepped on a rotten floorboard, which gave way and revealed the concealed space below. None of the Theta group's members were captured. The TNT charge in the cupboard -- placed as a last resort to destroy the equipment and, presumably, anyone searching the room -- failed to detonate. The trigger mechanism on the door did not fire. Had it worked, the explosion would have been catastrophic. The tightly packed wooden buildings of Bryggen, a wharf quarter that has survived since the Hanseatic era, would likely have been reduced to splinters.

The intelligence transmitted from this tiny room had consequences far beyond Bergen. Among other contributions, the radio transmissions from the Theta group provided information that helped the British Navy locate and eventually sink the German battleship Tirpitz -- the largest warship in the German fleet and a constant threat to Allied convoys in the North Atlantic and Arctic. The Tirpitz was attacked repeatedly before finally being sunk by RAF Lancaster bombers in November 1944. The intelligence pipeline that fed targeting information to the British ran, in part, through a hidden room on a medieval wharf in Bergen.

After the German raid, the room was gutted and its contents removed. When it was opened to the public in 1982 as a museum, the furnishings had to be approximated using wartime objects donated from across Norway. The only original items are a coffee table, a Hallicrafter receiver, a homemade high-frequency transmitter, copies of intelligence reports, and tasking messages from London. The guided tour is designed to convey what it felt like to work secretly against the Nazi occupiers in a room this small -- the claustrophobia, the constant threat of discovery, the knowledge that a cupboard full of explosives stood between you and capture. The museum's power comes precisely from its size. There is nothing grand about it. It is a closet where brave people did dangerous work, and it is preserved exactly at the scale of that courage.