"The entrance to the raceway tours are in Upson Park and below the gravel lot you were in. A flight of wooden stairs leads down to it. But the office where you sign up for the tours I believe is in Old City Hall, on Pine Street, next to the locks."I was there! First though, when I was in the initial parking lot I first looked towards downtown and saw off in the distance the top of an unknown-to-me building on Main Street that I had photographed earlier.
Then, as I was approaching my car, I saw the entrance to the wooden stairs across the way.
So of course I started down them and took a few pictures.
My wanderlust was starting to flag so I only went part of the way down the stairs before deciding it was time to leave. Some other time I'll be back, maybe on an actual tour of the Lockport Cave / Raceway!