When the Heart of Darkness is found, you will gain access to the underworld. Click/tap the medal in your fortress or click the Fortress button twice to get to your underworld.
The underworld is structured similarly to the fortress. In the center there is the Heart of Darkness. It feeds on souls that can be harvested from fallen heroes. After that, you have all the possibilities to gradually upgrade the underworld, improve it and make it useful for yourself.
There are several units, machines and locations available.
You can build the following buildings in your underworld:
- Heart of Darkness (main building)