This is a DukeMatch-only level not accessible within the game by normal means.
Secret Places (2)
Both secret places are hidden behind a lavafall. They're on opposite ends from each other. Use a jetpack to fly up and through the lava.
There are 5 combination switches scattered around the level, all very easy to find. Activating all 5 will open this pointless door harbouring yet another Battlelord. The first 3 are on the main floor in symmetrical positions. After activating the first 3, retrieve the blue access card from the center of the main floor (unless you are in DukeMatch, in which case you already have it). Enter the teleporters around the main floor until you find the area with the mugshot of Todd Replogle. Near his mugshot is the blue access switch which unlocks the top floor. The remaining 2 buttons seen in the image are on the top floor.