Hexen 64 

Cheat menu 
Pause the game:
and press C-Up, C-Down, C-Left, C-Right. Now a cheat option will appear at the bottom of the menu.

Level select 
Enter the cheat menu:
and immediately press C-Left(2), C-Right(2), C-Down, C-Top. 
If you entered the code correctly, you will hear the sound of rushing air.

Invincibility 
Enter the cheat menu:
and immediately press C-Left, C-Right, C-Down. If you 
entered the code correctly, you will hear the sound of rushing air.

Full health 
Enter the cheat menu:
and immediately press C-Left, C-Up, C-Down(2).
If you entered the code correctly, you will hear the sound of rushing air.

Walk through walls 
Enter the cheat menu:
and immediately press C-Up(20), C-Down. If you entered the code correctly, you will hear the sound of rushing air.

Kill all visible enemies 
Enter the cheat menu:
and immediately press C-Down, C-Up, C-Left(2).
If you entered the code correctly, you will hear the sound of rushing air.

All keys 
Enter the cheat menu:
and immediately press C-Down, C-Up, C-Left, C-Right.
If you entered the code correctly, you will hear the sound of rushing air.
Now enter the collect menu to activate the code.

All weapons 
Enter the cheat menu:
and immediately press C-Right, C-Up, C-Down(2).
If you entered the code correctly, you will hear the sound of rushing air.
Now enter the collect menu to activate the code.

All artifacts 
Enter the cheat menu:
and immediately press C-Up, C-Right, C-Down, C-Up.
If you entered the code correctly, you will hear the sound of rushing air.
Now enter the collect menu to activate the code.

All puzzle items 
Enter the cheat menu:
and immediately press C-Up, C-Left(3), C-Right, C-Down(2). 
If you entered the code correctly, you will hear the sound of rushing air.
Now enter the collect menu to activate the code.