Agartha

Agartha is a location in Conduit 2. It's where Michael Ford finally defeats John Adams.

Story
The battle continues in Agartha, where Michael Ford finally kills Adams. After he takes Adams' energies into the All-Seeing Eye, the device appears to go haywire. It then sends a message to a spaceship waiting in the outer reaches of the galaxy.

Back in Agartha, more humans wearing the Destroyer Armor emerge from the conduit, two of which are former Presidents George Washington and Abraham Lincoln. They announce that they are there to help. ("Agartha")

Enemies

 * John Adams

Real-world
Agartha is a legendary city in the real-world. It's believed to be located within the Earth's core.
 * Wikipedia page: Agartha