[Arthur catches the end of the rope and dives, needing to go fairly deep to tie it down before he surfaces again.]

It's fairly deep, but not unmanageable for someone else, I don't think. Too labyrinthine to really navigate without an air supply, though. I could try something if you'd like to see some of it, but I'm not as good at forming up hardwater constructs as my wife is. The Trident of Neptune isn't really made for precision magic.