Polyhex

Decepticon Headquarters is the structure that serves as the primary base of operations for the Decepticons on Cybertron.

Generation 1 cartoon
The dome-topped building known as Decepticon Headquarters on Cybertron was where Megatron planned to ambush Optimus Prime's energy-hunting expedition four million years ago. Before leaving, he told Shockwave to get off his shelf and watch the planet in his absence.

Four million years later, Shockwave was still doing just that.

Decepticon HQ contains a tower for sending and receiving passengers and cargo via space bridge from Earth. Occasionally, it would get hijacked by the Autobots for their own purposes. Usually, this would result in some damage to the base, and pain for Shockwave.

For some reason, the base contained or was connected to ventilator shafts, which could be used by smaller-sized beings to escape trap rooms connected to the base. At one point, the base held the duplicate computer used to control the hypno-chip slaves on Cybertron.

It also served as storage for the Decepticons' dwindling cache of energon.

MUX History
Shockwave and Cyclonus currently rule most of Cybertron from Darkmount, the fortress capital of Polyhex.

In 2012, the Dweller was released from beneath Cybertron, and when his thrall Hubcap was taken into Darkmount, the Dweller followed, laying seige to Polyhex.

Shattered Glass
In the Shattered Glass universe, Polyhex was a center of learning before Optimus Prime's brutal attack. Since then it has been militarized and serves as a rallying point for those who would stand up to Emperor Prime's wave of conquest and oppression.

Its capital is Darkmount. Cyclonus currently uses Darkmount as the Decepticon base of operations.