An easy way to get there, is while flying through Undercity on the bombing quest, log out, and log back in. It will teleport you just outside of Undercity.

Then fly literally on the Wickerman to put it out. If you don't you might not be able to reach it, or will have to fight guards for a while until you can mount again or are killed.

See? Easy.
Edited by Litlemouse on 10/22/2012 10:27 PM PDT