the long tunnel, but that is definitely onr of the highlight's of the dive. The actual "Devil's Throat" is a very tight drop off that requires excellent buoyancy control.
Right after you go through the tunnel (the tunnel is approximately 50 ft long, and is dark), you turn up to go into the cathedral. When you get to the cross, you go left and then left again (you are headed back towards the wall). Right as you are about to exit the cavern, you take another left into a small opening. THIS is the "throat." It requires you to swim into the opening, drop straight down (by exhaling basically) and exit to your left...shaped like a throat...sort of a downwards u-turn for lack of a better description. Once you drop down and turn left, you are now back in the cathedral area. You'll see the cross again and then there are several paths to take from there.
It is definitely NOT a dive for novices and I NEVER take anyone there without diving with them at least a day or two first to assess their skills. This dive requires excellent air consumption, buoyancy control, and a computer...no exceptions.