The Onyx mirror sometimes show up at a player, the player can then "touch mirror" to enter it.

The mirror contains a couple of distinct areas:

• tunnels (with Time Lord and Time Warrior)
• Village with a tavern, and Jhordie Aeln
• Tundra

I believe there is also a Rune Castle here...

Upper area and Tundra:

All south over the bridge, there is a tomb

• open tomb, and there is a message
• open tomb again, and you get attacked by wraith lord
  • Scroll of Soothing