Oblivion Gates are the gateways created between Mundus and the Oblivion planes. They are firey, magical portals that facilitate travel between the two planes. The strange humming, whining noise they emit can be heard before the gate is even found. The Oblivion Gates have been created by the Daedric Prince Mehrunes Dagon. He created these allowing the Daedra to roam and conquer Tamriel while causing widespread destruction and chaos.