The portal is located in the Valley of Spirits, next to the Portal Trainer npc.
The portal trainer and the portal are on the second floor of a Troll hut at 34, 70 ... it is above the platform with the blue flaming skull pile.
There is also a portal in The Cleft of Shadows beside the portal trainer, at the Arcane Enclave at 47, 92
The Blasted Lands is a mid-level zone in the Eastern Kingdoms. The alliance have a base there. The dark portal is also located in the blasted lands. It is the portal to The Outlands.
There's a portal to Outlands in Blasted Lands at the Dark Portal. To go through you need The Burning Crusade. ---- To get to the dark portal once you are 58, you can take the portal that is next to every portal trainer in the major cities (capital cities, ie, Undercity, Ironforge, Stormwind). You must be 58 to use these portals.
Next to the mage trainer / portal trainer
eastern kingdoms, in the blasted lands, south of nerthergarde keep.
The Dark Portal is south of Netherguard Keep in Blasted Lands which takes you to Hellfire Peninsula. The Portal bridged the distance between the worlds of Azeroth and Draenor, which opened the flood gates for the horde to enter Azeroth which began the first War
From Azuremyst Isle, walk or take a flight point to the Exodar. Find the mage trainer, where there's a portal to Darnassus. Take the portal, which will lead you to Darnassus' Temple. Go out the exit and move forward to the bank, where you turn to the pink portal to the left. You will arrive at the docks - take the boat to Stormwind from there.
Easiest way is to take the tram from Ironforge to Stormwind.
some have seen it in stormwind. in the canal near the instance portal that has the cage over it.
Netherguard Keep is an Alliance fortress built in the Blasted Lands. On its high vantage point, its Magi and soldiers can keep close watch on the Black Portal and send through troops to Outland beyond.
Stormwind was created in 1984.
There is no direct travel route from Northrend to Outland in the standard fashion. Some quests do allow transportation to Outland (the part of the questline involving Crusader Bridenbrad provides a portal to Shattrath; never turning in the quest allows this to be reused) but otherwise there are no permanent routes. The easiest way is to go to Stormwind or Orgrimmar and take the portal to the Blasted Lands, which is a short way to the Dark Portal and Outland. Some professions, most notably Engineering, provide a teleporter device to one single location in Outland (Area 52). Having completed the questlines for Akama, leading to being asked to kill Illidan, awards the player with the Blessed Medallion of Karabor. This item provides a teleport to the Black Temple in Outland. Mages of sufficient level can teleport to Shattrath, and are also capable of creating a portal to Shattrath for other players in their group.
There is one in Trade City of Stormwind right in front of the bank. Hope that helps!