Level Design - the Cave

Before I get onto thinking about the design of the environments in my telling of the story, I thought it a good idea to get a basic understanding of the layout of some of the play area. I've made this overhead map of the arguably the most interesting environment: the cave. Key points from the story need to be conveyed: there are three distinct areas, each with a different 'treasure' and guarded by a different monster. These areas are of course connected by the central chamber, which the soldier enters through the tree.

Each area needs to have a distinct visual style differentiating it, but also appear consistent with its brothers.

In the story, the soldier goes into each area and fills his pockets with the treasure he finds. As he finds more valuable items, he replaces what he finds. Clearly for this to make sense in the context of a game there needs to be a structure of gates to ensure the player doesn't skip straight to the last tunnel and most valuable treasure, missing out the majority of the level in the process.

When the player first spawns in the central chamber the route into two of the tunnels will be blocked; only by methodically venturing around the caves will they find the items they need to access the rest of the level. In the first chamber the player finds dynamite which can be used to destroy a boulder blocking the second tunnel. In the second tunnel the player finds a ladder which is used the navigate a chasm preventing access to the third area.

These puzzles also factor into the combat. As the monsters appear later in the story they obviously can't be killed at this point. Therefore, while the player character has access to a rifle for ranged combat and it's bayonet for melee combat, the monsters cannot be defeated merely by pumping a certain number of bullets into them. The player needs to use their environment to defeat the monsters. (I'm going to refer to them as monsters from now on for clarity.) The player can call up to their companion to drop down more ammunition at any point while in the central chamber.

The first monster spawns as the player is traveling back to the central chamber. It's arrival knocks columns over, impeding the player's quick access back to the central chamber and ensuring the player needs to defeat the monster first (perhaps a hole in the newly formed rubble must be crawled through slowly and the monster can easily grab the player character's foot and pull him out). 

The player must lure the monster to the chasm near where they found the dynamite sticks and force it off the cliff edge through repeated attacks (the monster would react to attacks by shuffling backwards a few steps each time, with perhaps an extra physical push needed at the very end).

The second monster is not defeated but rather avoided by carrying the ladder back towards the central chamber and using it to climb up to the ledge above (see 'drop down' on map image). However, the ladder is heavy and movement while carrying it is slow: the monster must be stunned by successive hits followed by a melee sequence. This causes the monster to be immobilised for a short time. Once the player character returns to the central chamber, he pulls the ladder up behind him, stopping the second monster's progress.

Monster #3 is defeated by shooting brittle stalactites on the roof of the third cave area. Eventually enough are destroyed that the cave roof collapses, destroying the cave floor between the monster and the player.

Once the player has explored all three areas, they must find the 'tinderbox' (or cigarette lighter in this transposition) before they are able to return to the surface. Some sort of puzzle involving information or items acquired over the course of the level in its solution would work well here.