Smoo Cave is unusual because it consists of sea- and river-made caves. This is the second chamber, eroded by the Alt Smoo river over the ages. You can go for free and see this view, but it's quite a long way from anywhere over fairly poor roads. And there are about 100 steps down (and back up!) the hill to get to it.
The orange area is the entrance to the third chamber, which has artificial lighting.