Below the station, the turbine shafts run deep — 150' or so — underground. We didn't make it that far (safety is a concern, no matter what it may look like) but we did get down maybe two-thirds of the way. Going further requires a greater level of committment and proper safety.
The image to the right is a cross-section of the plant. (Image was sourced from Niagara Falls Public Library site.)
Sadly, I have no interesting photos from the lower levels. It was nearly pitch black, and even my huge flashlight barely helped. I'll offer up these two in an attempt to display what it was sort of like down there. For perspective, in the second photo, the distance from the camera to the top of the image is about 100 feet.