Find the Epsilon Crystal in Castle Kriegspire is a main quest in Might and Magic VI: The Mandate of Heaven. You must have already gained access to the Oracle in order to receive this quest.
The Oracle is unable to help the party unless its memory crystals are found and re-installed. It asks them to retrieve the four crystals from their current locations and install them. The Epsilon Crystal is currently in Castle Kriegspire.
Monsters[]
Minotaur → Minotaur mage → Minotaur king
Agar's pet → Agar's monster → Agar's abomination
Flame drake → Frost drake → Energy drake
Walkthrough[]
The Oracle is located in the Control Center in the High Council building in the town of Freehaven. Castle Kriegspire is in the center of the volcano in the Kriegspire region.
Enter, and proceed forward the only way you can go until you come to a passage that branches off to the right (there will be minotaurs in a guard room with a window on the corner). Take that branch and follow it back until it tees into a cross passage with a large room straight ahead (you will pass a barred door to the right on your way, but it won't open - or necessarily even admit it is a door - at this point).
Take the left passage and follow it around the large room area (that you should see on your map), until you come to some stairs. Count them as you go up; the eleventh one is a trap and you will fall through if you step on it, so use the X key to jump over it.
Continue forward until you enter one of the large rooms on a balcony. Turn right on the balcony and go through the first doorway to another room's balcony. On this balcony, turn left and continue around until you come to the first doorway. Go through, turn left, and go through the first doorway here too.
You should be in the center of the four rooms, looking at a column. Walk around to the other side of the column and push the button switch on it.
Return to the door you passed up that was barred and unopenable before. (If you're going to just jump down into one of the rooms, save your game first.) The barred door will open as you approach it. Go through and turn left when you have a choice. Follow that passage around until you are on a balcony area overlooking a sunken room. You should be able to see the Epsilon crystal mounted on the wall of the sunken room.
Jump down into the room to take it. There is a teleporter there to get you back out. Once you've been teleported, take the stairs in front of you and open the door at the end for a shortcut back to the entrance.
Take the Epsilon crystal back to the Control Center and place it in the mounting that is up the ramp immediately to your right as you enter the control room. (Ensure all systems are turned on first.) The crystals can be installed in any order and you don't need to wait until you have them all to get the reward.