There is a device near each of the doors. It looks like the one that triggered the raising-spears traps but it is canted over, as if broken. Triggering it does not appear to do anything. However, beyond the third door is a Mario-skillz series of platforms you need to jump across and the spikes below are active. Not clicking the three devices does not seem to do anything, either. Additionally, a Protection Stone to one side of the third door also does not seem to do anything.
What you cannot see, however, can thwart you. You must trigger all three switchesyou cannot flip the Protection Stone and break the Seal Stone behind which are two Treasure Chests.
After the jumping is a large black crystal. Smash it. This opens the Stage Portal.
Up the stairs is a door with a Stone next to it. When you enter the courtyard another gate to your right opens, showing a stone beyond it.
Cross the brodge and trigger some skeletons. Kill them and get a message that you can now break the Seal Stone. Activate the stone before the angel statue, then return to the previous door and click the stone there. This closes the door to the angel garden and summons some skeletons and a minotaur. Kill them, then activate the stone so you can activate the stone at the door in the previous area. Also, down the steps to the right of the Angel Garden is a Treasure Chest.
Up the steps you find another courtyard and another large black crystal blocking the door. Entering the courtyard summons a minotaur guardian and a bunch of skeletons. Kill them all and the crystal explodes, opening the door to the next stage.
IF you have the quest Krag's Challenge he will have a cutscene after the Minotaur is dead, then a brief fight. He is not as good as he thinks he is.
Big. Fast. Mean. Even on Easy this was really tough for a level 18 Mercenary.
He charges (no defense), leaps into the air and slams down on you (no defense) and fires spikes from his tail (can be avoided).
After he charges, assuming he missed you, you can dart in and pummel him with special attacks. Just survive long enough to whittle him down. An HP Potion on hotkey would be a good plan.