The level apparently takes place in the volcanic crater of what may be presumed to be Hell's eponymous Mt. One is filled with Lost Souls, the other with Imps. Read more at other points of interest. Made in about 2days. Erebus: Blue key - YouTube Shows how to access the blue key in PC Doom/Ultimate Doom level E3M6, Mt. Standing near the marble building where you should go. This level contains a secret exit leading to E3M9: Lake of Fire .