I don't think anyone has posted about it (or maybe even discovered it yet), nothing came up on search, so here goes.
What you'll need:
-TBC Rocket boots (anything else isn't fast enough)
-Parachute cloak
-A way to avoid fall damage (Divine Shield, Iceblock, spammable Slowfall, Rogues and Druids *may* make it with falldamage reduction. Unfortunately I can't test that)
1) Start at the picture below:
2) Rocket boots and parachute cloak towards the mountains highlighted in the picture.
3) Your parachute cloak will run out as you're flying over the area you want to be, so prepare to negate your falldamage with a levitate, slowfall, iceblock or divine shield. Alternatively, soulstone/resurrect yourself if you are a Warlock/Shaman. Once you've done that, you should be here:
Interesting stuff:
An interesting note: there is a small Unknown area at the Ruby Dragonshrine as shown below:
Afterthoughts:
It is possible to reach the Crystalsong Forest side if your faction's Airship is still docked there. Also, it is likely that you can utilize the levitate-wallwalking to get out aswell, although I couldn't test because I didn't have a Priest handy.
Also, do note there is a considerably large instant-death zone around the vicinity of the actual instance itself. Entering it will quite obviously cause you to die in a most horrible fashion.