Dalaran Hearthstone
Source: Quest. I case you have lost your hearthstone, you can find a portal in Stormwind in Stormwind Keep.
The 
Dalaran Hearthstone is a toy obtained through the Legion introductory questline that teleports you to Legion Dalaran.
Guide awaiting review
Start Legion Intro Quest
Visit the Hero's Call Board in Stormwind's Trade District (Alliance) or the Warchief's Command Board in Orgrimmar's Valley of Strength (Horde) and pick up The Legion Returns from the Broken Shore option labeled 'Fight The Legion'.
Turn In and Travel to Dalaran
Head to Stormwind Harbor (Alliance) or the front gate of Orgrimmar (Horde) to turn in the quest. If you have already completed this questline on another character, Recruiter Lee (Alliance) or Holgar Stormaxe (Horde) will offer you the option to skip the scenario and teleport you directly to Dalaran.
Complete In the Blink of an Eye
Once in Dalaran, turn in the final quest In the Blink of an Eye. Completing this quest unlocks your Dalaran Hearthstone.
Alternative: Fly to Dalaran via Azsuna
If you cannot access Legion Dalaran through the quest boards, take the portal to Azsuna from Orgrimmar at 58.86, 89.53 (Horde) or from the Wizard's Sanctum in Stormwind at 46.86, 93.40 (Alliance), then fly north to Dalaran floating in the sky.
Collect from Amisi Azuregaze
Go to The Legerdemain Lounge in Dalaran, just north of the Chamber of the Guardian, and speak to innkeeper Amisi Azuregaze at 49.7, 39.97. Select the option 'I seem to have misplaced my Dalaran Hearthstone' and she will hand you a replacement Dalaran Hearthstone. Boosted characters who skip the Legion cinematic can come directly to her to receive the hearthstone without completing any quest.
Tips
If you receive a 'you can't use this' error, the Legion introductory questline has not been completed or skipped on that character — return to the Hero's Call Board or Warchief's Command Board to begin it.
See video guide for a full visual walkthrough of the steps above.
