WoWwiki informs us that this is one of the dimensional gateways Magtheridon used to summon demons from the Twisting Nether, at least until Illidan shut down the gateway. Thanks to Hunterbert of Chou Hadra on Alonsus for sharing this snippet of history with us!
Do you have a screenshot that captures a moment in Azerothinan (or Outlandian) history? We'd like to see it on Around Azeroth! All you have to do is e-mail email@example.com with a copy of your screenshot and a brief explanation of the scene. You could find your pictures and story featured next!