You see a dark black screen - silence - sometimes a rumbling, getting louder then dying away...
Now - from the edges of the screen - you can see big blocks appearing - formating to big strong walls. Must be a sort of a room? (you think).
You have no idea what's going on there...
And then - A FLASH OF LIGHTNING - a man in this cave - a sort of a soldier.
Look like a spacesuit with a helmet and he's carrying a big gun! (

)
The man starts to run - he seems to be in a hurry.
He's running to the left where you can see this room has an exit fading to a long corridor or a winding cave...
There appear some kind of foes (robots/aliens/maschines/traps) attacking the lonly man on his run but also sometimes some goodies (health packs, ammo packs, ...) supporting the struggle of the man...
So what is this man?