How do I get to Fire Lich in Soulfire bastion?

[Dr. Atomic]

I enetered the dungeon cleared most of it but can't find an entrance to the boss? There are only doors to add difficulty modifiers. Where is the boss door?

[PrEzi]

Youe need to pass two levels to reach the boss... so basically one door with modifiers + harder monsters and then the second doors with modifiers on the boss itself.