You can climb the pillars near the bridge, not the ones near where the ogres spawn, but the ones near the totem panels. By doing this no enemies can melee you, but you have to snipe any ranged enemies as soon as you can. Once the Wizards spawn kill them to spawn the ogres. Kill one ogre then run towards the door there is an area where you can climb up to protect yourself from the melee enemies and the ogre has trouble hitting you, finish him off to unlock the door.