In reply to Tony Buckley:
It really is an amazing canyon. One of the few places I have just lost my bottle and refused to abseil in, as when it came to actually committing I just wasn't feeling it.
The commitment of abseiling in to do the south rim routes is immense. The idea that if something goes wrong you will need to abseil off, back into the canyon, find the river crossing point, cross the Tyrolean, find the correct gully to escape up out of to the north rim and then run to the ranger station/car to get help weighs on the mind.
The difficulty of this rescue from the north rim sounded bad enough.
There is excellent climbing though.