It's unique - diving Iceland, between two continental plates
Not relevant to this thread or to the tragedy described, but there is at least one other place to dive between two continental plates. I forget exactly which reef, but at Tiran in the NE Red Sea the two continental plates are presented as sheer rock faces that look as if they were cut with a saw. Eventually they will be on opposite sides of an ocean. The water's a tad warmer than on the Icelandic dive.