Dungeons 4

The key for this one is that the Arcanium must be enclosed on all sides by walls. It cannot be built out in the open and be efficient. It should have one small opening to enter the room. Once that is complete, it should give you 90% efficiency. Unlock the door through research. Then build a door at the opening at that will get you to 100% efficiency.

I think the room may need to be square too. I would have to test that. But the size should not matter because I have seen 5x5 work and 7x7 work.

This can be done with the Arcanium that the game starts you with at the beginning of the stage. Here is step by step:
- First mine the corners of the room to make it a perfect square.
- Build the Arcanium on the floor tiles on the spots you mined.
- The room should now be square with walls. It will have once small entrance. And all floor tiles are Arcanium.
- Build a mana tower in the center (now sure it necessary, but part of the stage)
- Research the Door
- Build door at the one entrance in.
Done.

Once you've built a 5x5 Arcanium, Build a single Mana Tower.
This should get you to 90% efficiency.

Add a door to the entrance of the chamber and the achievement will unlock.

Happy Hunting