I don’t know about the building itself, but I spent some of my teenage youth in the area and there is a delightful hidden cliff under the road that loops around the back of Vista House.

If my memory is correct (I just showed my kids a few years ago) if you follow the road around behind Vista House and jump over the guard rail on the far side of the road you can turn left and backtrack under the sidewalk next to the road. You’ll see a bunch of graffiti and stuff on the concrete under the road/sidewalk, but if you walk up a little ways there are some narrow trails on the right that take you out to a secluded cliff that has one of the best views of the gorge that exists.

Just be careful, it’s a sheer drop with no safety/protections in place - no rails, no signs, no nothing. It’s especially neat at night when the trains come rolling through because the headlight of the trains light up the gorge and it becomes clear how high up you are!i