So I descended 650 meters in twenty-five minutes, certainly my all-time record (at least until I cut my shin on the Black Giant, but that’s another story). I panted along the shores of the radioactive Limmerensee until I was stopped by a cliff that dropped straight into the water. The trail ran right under a black iron door in the cliff.

The tunnel. God damn it one more time. I don’t like tunnels. I approached the door and looked at a page taped to it. The printed message, in German of course, had words so long they crossed the whole page. I couldn’t understand any of it. Apparently my streak of German had ended in the great exchange with the hut keeper. Fly you! I had flown.

I turned the handle and pulled the door open. There was a light button just inside the door, and when I pushed it a line of bare bulbs came on overhead, illuminating a tunnel about nine feet high and not much wider. There were metal tracks, like tram tracks, laid on the tunnel’s stone floor.

I stepped back out into the sunlight and tried to read the sign again. No way. Inside, a simpler note by the light button told me that the lights would stay on for twenty minutes after I pushed the button. Back outside I checked my map again. Yes, the tunnel was between two and three kilometers long. Say a mile and a half. I could run that in less than twenty minutes. And I would have to, not only to beat the lights going off, but in order to get to the cable car station at the other end of the tunnel before 3:45-because it was now 3:31!

I banished my distaste for the tunnel and stepped back inside the iron door and let it clang shut behind me. I hit the light button one more time and started jogging down the stone floor between the tram tracks.

Quickly I was far enough down the tunnel that I couldn’t see the door behind me any more. In both directions the light bulbs ran together into faint lines, which eventually disappeared entirely in the gloom. There were leaks in the rock ceiling, and occasionally I ran under little curtains of dripping water; often I stomped through puddles between the tracks. Getting winded, I checked my watch; I had been running three minutes. Probably my initial pace had been a bit fast.