ToME: the Tales of Maj'Eyal

I went to kill Urkis from mage city, and in the little square stage you first arrive at, there were lots of graves, so I opened one and fell in a hole, beat the baddies and achieved "Restless Dead" achievement. when I cam back up out of the hole, I was outside the level floating in blackness! Tankfully I could recall out to the world map, but I should have appeared back on the little area leading to urkis.

btw, is there any way to get to urkis now?

You should be able to get back to the Tempest Peak by whatever method you used before.
eg. you can keep getting teleported there until Urkis is dead.