You can unlock a Cheat called 'Area 51 Mode' then enable it in the secrets menu! This will change the Deadwings into ufos!
Go to Deadside: Marrow Gates. At the beginning of the level, go to the left and climb up the blood waterfall. Open up the Shadow level 10 Coffin Gate (120 Dark Souls). Along with this cheat you will also get the Book of Shadows.
N64 and Dreamcast Locations:Edit
Not on these versions.