I’ve never noticed that trapdoor next to the sidewalk before. I walk there every day but that piece of concrete and metal in the middle of the grass verge was new to me. The 80x80 centimeter hatch had to be the entrance to a duct, probably into the water system of the city.

Today, it caught me. Was it there forever or did it just appear. No, such things never just appear. What was I thinking? But in the evening, I got restless. I had to go back.

I opened the trapdoor with a lever - I brought one together with a flashlight, a fully charged phone and my wellies on my feet. The next thing I saw was light. The underworld was lit. That surprised me. I packed away my torch, climbed down the metal ladder that was mounted on one side and closed the hatch.

Looking around, I noticed that this could not be the waste water system of the city. Everything was clean and there was no smell except for some stale air. I stood inside a curved hallway that went downwards, deeper into the earth. I started to walk.

The lights on the side of the hallway were most interesting. They had been mounted every 20 meters or so and all of them looked different, like a lesson in industrial design over the times. There were lamp styled from a whole century. Starting with old torch holders over gas lamps and early electric installations up until flat LED plates. That hallway was old and always used. But other than that I saw no features. No doors, no other ladders, no rats, not even dirt.

After a while I was looking at my phone. As expected, neither GPS nor Internet were working, but it counted the steps, must have been two kilometers since the start, always downwards, sometimes flat, sometimes steeper.

Not knowing where this would end, I decided to end this experiment for now. I had clearly brought the wrong equipment. So I went back up. This time, it was more exhausting. But I finally reached the ladder again.

I climbed up and stepped out again. But it took me a while to realise that I came out at a very different place more than a kilometer away from my starting point.

Later in bed I had to think this through. There was no junction that I could have missed. There was als no second ladder. But how else would I get there? What a weird experience. I made plans for my second field trip until I fell asleep.