The Sea of Rust is an area on Cybertron.
After obtaining the Omega Keys, Megatron went to the Sea of Rust to find the Omega Lock. He and his Vehicons were attacked by the Autobots, who reclaimed the Keys and managed to locate the accompanying Lock.
After getting the keys back, Megatron activated the lock and restored a nearby building with it. Optimus then hit the lock with the Star Saber, exploding it and devastating the immediate area.
Knock Out and a small team ventured back there to search for discarded relics. They were joined by Shockwave, who had spotted the huge energy surge created by the Omega Lock and driven over from his laboratory.
When Cybertron was restored, the Sea of Rust was transformed into a habitable landscape for Cybertronians. It was the scene of a battle between Ultra Magnus, Smokescreen, Darksteel and Skylynx. That battle resulted in Magnus being gravely wounded. Much later, after Bumblebee told Predaking of their existence, the Predacon leader searched the Sea of Rust for his two new brethren, using his flame breath as a beacon to attract them. However the beacon instead drew in a Unicron-possessed Megatron and Predaking, having previously been betrayed by Megatron, fought him but was defeated.
The ancient map room managed to stay intact during the mysterious disaster that transformed the area surrounding it into the Sea of Rust.