Megatron's main fortness is known as Kolkular.
Built on a plateau three times the size of Iacon, Kaon was the industrial heart of Cybertron, where nameless members of the low castes toiled endlessly. It was a dark, smoking mess of a city that was impossible to navigate without the Communication Grid. The High Council ignored the emerging gladiatorial combat in the areas surrounding Kaon, acknowledging it was the inhabitants' only escape in their lives. A champion taking the name Megatronus emerged. This Megatron took control of the gladiators and formed the Decepticons. His base was a single, large pyramid.
During the war, Optimus Prime, Jazz and Prowl rescued Sentinel Prime from the pyramid, which had become Kaon Prison. Megatron and Shockwave had made a deal with the Underworlders to chain the prisoners underground. The Autobots were only confronted by two gibbering guards, which Optimus presumed was the toll of Dark Energon.
Before the Great War, Arcee explored the tunnels in Kaon. In the present, she returned with Cliffjumper to find Starscream, who had constructed a space bridge there. Cliffjumper distracted Starscream's Vehicon forces while Arcee overloaded the space bridge's controls. She, Cliffjumper and Starscream jumped through the space bridge portal to Earth before it exploded.
Megatron honed his gladiator skills in "the pits of Kaon". He took Kaon in the war for Cybertron as a capital, however he was completely unaware that a powerful device called Vector Sigma was right beneath his feet.
When Bumblebee used a cortical psychic patch to enter Megatron's subconscious, he found himself in a recreation of the city. In Sick Mind, Attempting to find Vector Sigma, Jack Darby and Arcee were led to Kaon by the Key to Vector Sigma. They managed to wake up an Insecticon sentry which attacked Arcee while Jack went below ground to the Vector Sigma chamber. He was able to download the contents of the Matrix from the computer, despite interference from Scraplets, and he and Arcee headed back for the space bridge.
Megatron initially named his new Earth fortress "New Kaon" after his capital on Cybertron Darkest Hour but later changed his mind and renamed it "Darkmount".
After Megatron's death and the Autobots' victory and restoration of Cybertron, Optimus promoted Bumblebee to warrior class in the same pit of Kaon where Vector Sigma dwelled beneath. To celebrate the occasion and the beginning of their reconstruction of their home, Wheeljack blew up the statue of the deceased Decepticon warlord. When Megatron is alive, he left Kaon and exiled from Cybertron after refusing to continue the Decepticon cause.