step 1: be a gnome mage with blink or use some means of shrinking yourself to gnome height (pygmy oil, noggenfogger elixir, gnomish world enlarger, etc.) and have your hearthstone on cool down
step 2: go into the Ironforge bank
step 3: jump onto the vault handle behind the tellers
step 4: carefully jump across the pegs in the vault door
step 5: jump onto the upper hinge to the vault door, to do this you must first face slightly away from the vault door so you don't hit your head on the ceiling
step 6: walk around the peg and stand between the vault door and the ceiling
step 7: either cast blink or auto unstuck while your hearthstone is on cool down
step 8: you should now be standing on top of the vault door, move to your left and face north
step 9: be at full health and jump straight north, you should land in Old Ironforge