Megatron's castle

Megatron's castle is a Decepticon headquarters. It's not always Megatron's, though.

Dreamwave Generation One continuity
Megatron's castle, then known as just "Decepticon HQ", was used by Shockwave after Megatron's disappearance. There, he communicated with Scorponok and Ratbat abut Decepticon affairs. Soon after, he had a meeting with the Race Track Patrol that ended with the Patrol leaving the Decepticons.

Shockwave soon moved to another building.