Once I beat the game, it had something written in it. It said of a secret room where a great hero was buried, anyone else found this or know anything to clue me in, I'm currently stumped.
The room where the great hero was buried is right next to the book. as soon as you see the book, you'll know you're in the right area. Just look for the weird designed sub-room. It also has nothing to do with beating the game, the text is currently bugged. You will find the following things, a guaranteed Interdimensional axe, a crappy helmet, and a random artifact. The axe and the rocket launcher are both hints to the game Quake, all those years ago. Doom had a rocket launcher, but it didn't have an axe. And that axe is 100% a replica of the Axe from Quake.