On our way out of Hellfire Citadel, we figured we'd see if we could find the entrance to Hellfire Ramparts (which in retrospect seems kind of silly... ramparts should be on the outside of the fortress). We jumped down to one of the walkways below and made a disturbing discovery - there was no way back up, and the doors leading back into the Citadel had been sealed with solid stone. We continued with our descent by jumping down to the catwalks and gangways below until we ran out of them and were left stranded high above the canyon floor with no way down... except one.
Carefully choosing our spot, we jumped. Plummeting hundreds of feet, death seemed assured despite the Rogue's innate Slow-fall ability. Fortunately, we narrowly caught the stone sill of a door set into the base of Hellfire Citadel. Suffering only minor bruises and abrasions, we thanked the light for its mercy and hopped down to the orange, dusty floor of the canyon. We noticed another instance entrance at the bottom of the Citadel, but could not enter it as we were neither level 70 nor in a raid group. This was clearly the entrance to the Pit Lord Magtheradon's lair, and was surprisingly easy to access (y'know, if we were level 70 and in a raid).