Star Wars Jedi Knight II: Jedi Outcast Easter Egg - A Long Time Ago... on Earth

This egg is well-hidden and can't be found without using cheat codes.

It's located in the first level of the Doomgiver starship. If you don't want to make it through the whole rest of levels just bring up the console by hitting SHIFT and ~ [tilde], then type "helpusobi 1" (without quotes of course; btw another funny thing) or "devmapall", press enter and type "map doom_array".

When the map loads, stay on your start position. Bring up the console again and type "noclip" (yeah, that's a cheatcode). Then just hold jump until you go through the ceiling.
Look up and enjoy -- it's a picture of our Earth being hit by a comet!