We arrived at a U-Bahn station in Berlin amongst a bustling flow of pedestrian traffic getting on and off the trains underneath our feet. A group of young people began to form as we were all waiting for the same tour of the bunker. Our guide soon arrived and produced a key from a large (and crowded) ring hanging from his neck, then proceeded to unlock an unassuming door built into the tiled wall. We entered a strange, transitory space between an off-limits subway station area, and a World War II era bunker. The entrance to the bunker proper was down a steep concrete staircase, fringed with white and red striped paint to clearly mark the concrete edges through thick dust and smoke.

The tour was in German so I didn't catch many of the facts or descriptions of things, but I was extremely happy to be able to tag along to see the place, and on top of that, we were given special permission to take photographs - this is normally not allowed due to the possible misuse of the images in Neo-Nazi circles. As the group moved down the staircase, we were allowed to hang back a bit to photograph the spaces without throngs of people in the way. Soon we were let loose to shoot the museum down here, but with a fun challenge - no lights! The old luminous paint on the walls glowed with a eerie green light, marking out the pathways and doors in the blackness.

I tried to get as much as I could with my flashlight and long exposures; we had been given news that a private tour of another bunker has been secured by Berliner Unterwelten. City workers were at the location to open the passage that led under the streets, and weren't going to hang around forever. We quickly packed up and donned bright yellow rubber boots of varying sizes, and waited for the train to arrive at the platform. Curious glances came from passengers and especially the tour group that just finished up, wondering what we were up to.

When our train dropped us off, we trekked up to the city street where crews unlocked a large metal grate. A black hole yawned before us, releasing an ancient dank, musty smell from within. We descended into a concrete network of rooms and hallways; most were filled with two feet of water. It was pitch black of course, and the only sound was a cacophony of dripping water that seemed to turn into a dull roar after reverberating off the solid walls. We were told that this bunker was last used as a secret passage for traveling under the Berlin Wall undetected, and that a corner of the wall was still visible inside. Unfortunately none of us found this piece, but it was still a fascinating trip through time - the ventilation and filtration systems still seemed to be intact, as well as a few other metal objects that hadn't corroded entirely over the years. We could have spent much more time in those dark cement catacombs, but the gate had to be locked up before the trains stopped running, so back out into the night we went.