Through the trap door, we could see a mechanical room about 18 feet below us, with no way down.

Toronto General Hospital (October 2002): It just ain't fair. Liz and I fell in love with TGH's Charlie Conacher Research Wing the first time we strolled through its empty hallways and set out in search of the gorgeous tower at its pinnacle. Now, a scant few months later, the hospital is rapidly looting every remaining item of worth for the wing and preparing to demolish it. The destruction of the hospital's most elegant and beautiful wing is a huge loss for everyone in the city, but especially for urban explorers. While the public is no longer allowed in the wing, Liz and I are doing everything in our power to document all its wonders for posterity. So far it's going very, very well.
      Armed with some anonymous tips from a very kind soul, we showed up early one weeknight. After climbing up to the fourth floor — which we found even more abandoned than usual — we struck out on our primary goal, the gorgeous roof tower, which was thoroughly locked away and inaccessible. We were a little disappointed, but consoled ourselves by exploring recently evacuated offices, clinics and locker rooms on the lower floors and in the basement — I think it's safe to say that we were the first to explore most of these, since the movers were sort of working around us.
      While this was fun and produced some good pictures, it was when we came to the bottom of a service stairwell that things started to get interesting. As we came down from the basement, I looked down and, seeing no stairs, said to Liz, "Awww, it doesn't go down any further."
      "Oh, it doesn't?" she said, brushing past me and moving to lift up an old iron trapdoor set into the floor.
      We peered down into a large, dimly-let mechanical room in a subbasement about 18 feet beneath us. "We have to get there," I said, and we set about doing so. Proceeding to the door in a far end of the basement that we'd heard might be a possible entry point, Liz prepared to push it open. Just before she did so, however, she peeked through the hole where the doorknob had once been and then turned to me and whispered "Oh my god!"
      "What?" I asked, as she began to briskly walk away from the door.
      "There was a dude, crouching down, right on the other side of that door!"
      That route blocked, we proceeded to possible entry point B, and here met with our first really unbelievable success. Heading down an old stone staircase, we found ourselves in the middle of long, hot, pipe-crammed steam tunnels, bending around corners and extending further than we could see in either direction. These steam tunnels are filled with a greater number of pipes than I've ever seen in a tunnel before; at points, there are so many pipes that they form a barricade against further progress.
      After a while in this area, we really wanted to see what was in that room with the crouching guy, so we headed back. The guy was gone, and he had turned off the lights behind him. We began to prowl around the room for anything interesting, but it looked like just one of the many hundreds of empty offices in the area. It was in a room to the side that we saw the sight that totally filled us with joy and wonder, however: a half-height door tucked away into the corner, with a metal ladder leading down a brick shaft.

It doesn't get much pipier than this, folks.