If you don't know how to solve the main EE, than this is the guide for you. First you have to collect the first record hidden on 5 specific spots and walk up to the room with the big skull. Now interact with the gramophone and the wall breaks apart.
Do this 4 more times and the wall is broken. The records spawn one by one after every interaction with the gramophone.

After that you have 2 Ways to go:
1. The teleporter to Pack A Punch and the Summoning Key (Beware that the summoning key takes one weapon slot!)
2. The EE room with the hieroglyph stones

On the entire map there are 5 random hieroglyph stones with random symbols. The numbers next to the symbols tell you in wich order you need to shoot the stones in the EE room.
After you shot all of the symbols in the correct order, the door to the endgame teleporter opens.
Now you need to throw the summoning key at the teleporter. The game ends.