Teleport to Dalaran Crystal
From WoWWiki
The Teleport to Dalaran Crystal is located in Violet Stand [15, 42] on the western edge of Crystalsong Forest and teleports to the Teleport to Violet Stand Crystal in a portal room in eastern Dalaran just behind 
Archmage Celindra <Portal Trainer>, but only if you have used the Dalaran crystal first.
It is involved in the following quest:
Patch changes
- Prior to Patch 3.0.2, it teleported to the placeholder Teleport to Ruins under Dalaran Crystal and was located in open, columned ruins in central-western Crystalsong Forest at the end of the road starting from central-southern edge of Crystalsong Forest that comes from The Crystal Vice in northern Dragonblight.
