There are several ways to get there. If you've visited before and have activated the lodestone north of the city, you can simply use that. Otherwise you have several choices.
1. Via Mobilising Armies - Once there, run straight East to Oo'glog.
1a. Teleport to Mobilising Armies using the teleport in the regular spellbook (Level 10 Magic required). 1b. Teleport using a Duelling Ring (Option 3). 1c. If you've completed the quest Tree Gnome Village, use the Spirit Tree network to get to the tree outside of Mobilising Armies.
2. Run South from Yanille - This option will take a little bit of time (a few minutes). Be sure to watch out for aggressive NPCs such as Ogres and Wolves.
Once you've gotten to Oo'glog, be sure to activate the Lodestone North of the City (outside the West Entrance) so you can teleport directly next time.