Spire Village

Approach the circle of huts - a Titan will attach you. The best tactic is to use the
heat-seeking Eightball to bring him down.
Once he's dead, search all the huts for pleanty of ammo (you'll need em!) and supplies
and then make your way up the hill.
You'll encounter two more Titans - kill the Skaarj, and, once at the Sunspire Walls,
jump up and push the keyhole to open the gate.