Magma was an island several miles off the coast of Greece which serves as the base of operations for the evil Mythos Cyborgs. It is also a central narrative location that makes up most of the Mythos Arc of the Cyborg 009 manga and the staring off point of the Cyborg 009 part of the Cyborg 009 vs. Devilman OVA film.
The island has sandy beaches and a massive active volcano at its center with many Ancient Greek buildings and architecture dotting the landscape, including a temple near the volcano. It also houses hidden access points to a large underground Black Ghost laboratory, where Dr. Gaia and Dr. Uranus conducted experiments and research on energy as well as perfecting new technology for their Mythos Cyborgs.
The island is first seen in the first few minutes of the OVA and many of its structures were damaged due to the conflict between the 00 Cyborgs and the Mythos Cyborgs. With most of the 00 team beaten into exhaustion and all the Mythos Cyborgs but Helena and Apollo dead, Joe Shimamura aka 009 valiantly fought on the island to stop Apollo's rampage. Their battle lasted until dusk and before Apollo could deliver the final blow to a weak and exhausted 009 on top of the volcano, Helena stopped her brother and then pushed 009 out of the way. As the volcano had another seismic shift from its eruption, Apollo and Helena both fell to their deaths. Apollo's still active pyrokinesis before death compounded with the volcanic eruption caused the island to break apart in a violent explosion and sink into the ocean.