There is one part where you are invited to walk on a catwalk that's very high up (an outdoor staircase sort of like a fire escape). My recollection is that walking on it is not mandatory for the tour, but I'm not absolutely certain of that.
You're also invited, but not required, to look over the edge of the dam from the top, which is also very far down.
This is correct. If you don't like heights, that's definitely not a reason to skip the tour, but you'll miss out on one piece (that I enjoyed).