After activating the last totem in Unclean Totems, the inner door unlocks. Behind that door is a demon. Simply defeat the demon and use the portal in the corner to teleport out.
The small portal will take you just outside the entrance to the Lost Crypt. Make your way back to the Zombie Camp and talk to Officer Bramus.
Perfect. Here's your reward.
Fantastic! You actually rid the crypt of demons?! That means we won't have to do it ourselves! I am delighted! And my... brave soldiers are delighted, too. Here take this small token of my appreciation.
The The Lost Crypt chain quest is now complete.