Dungeon Obstacle Ideas EL 10-15

[DragBornPaladin]

I'm currently running a campaign in a homebrew world based on the core 3.5 books and heavily influenced by both of the Fiendish Codices. I'm going to have the party investigate an abandoned cult of Orcus that sits high on a mountaintop near a major human city. The cult was destroyed long ago, but a lich who was too powerful for the ancient crusaders to overcome was locked deep inside with the rest of the undead horrors by flooding a shaft with Holy water (endless water supplied by an artifact) permanently locking away the lich. I need some ideas for dungeon obstacles for the section after they have swam through the holy water to explore the cult's fortress.

Thank you in advance for your input.