Semue Iera

From LSWiki

If you enter from Tainaron, you start at -19, 2, 0.

Semue Iera is at (3,3,3) River Tethys. You can also do "go 5e, 6n, u, 3n, 4e, u, 4e, 4s, u, 4e, 4s, 5e" from the Hoop of Fire in Tethys. (flight may be required. return trip: go 5w, 4n, 4w, d, 4n, 4w, d, 4w, 3s, d, 6s, 5w )

Make sure you can gain knowledge of the gate, whether via lens of insight or otherwise. Mounts, unless they have the gate identified, cannot enter, so you will have to dismount.

You can read (not technically, looking at them works) the runes (do so twice) that are on the walls of the room, and if you have enough rune lore, you will identify Semue Iera automatically.

You will then need to "enter Semue Iera" to gain access to Obsidia.

 Take care you haven't exhausted your spiritual energy before attempting to enter the gate or the result will be rather painful
 "You feel a sudden lack of power within yourself as you realize that your reserves of spiritual energy are too weak to allow you to make the
   journey into Semue Iera safely.
 You are sucked bodily into the lightless depths of Semue Iera, your body becoming visibly twisted and deformed by the intense forces tossing
  you about as though you were a mere toy.
   You are wracked by incredible agony.
   You have been stunned by the pain.
   You are pulverized.
   You have been stunned by the pain and trauma."

   After a moment, the knowledge that Semue Iera is composed of sixty-seven
percent force and thirty-three percent skiarax drifts into your mind like a
long-forgotten memory.