Getting to the Blue Key Slot (6)

At the bottom of the right elevator, you'll find Laser Tripbombs (proximity-triggered explosives). You can destroy them by throwing a Pipebomb into the elevator and detonating it after you exit, or by riding the elevator down, alerting the Enforcer (an enemy type), and quickly returning to the top. The Enforcer will follow and detonate the bombs, destroying himself in the process.

A Large Medikit (health item) is located at the entrance to the Blue Key Door.

Ascend the elevator and open the Blue Key Door.

You will enter a room bathed in red light, populated by Sentry Drones (flying robotic enemies). Take cover (press the cover button to crouch behind walls or objects) in the doorway before proceeding further into the room.

An Small Medikit (health item) is present in this red light room.

To the left of the red light room, there is another room containing two Enforcers and Devastator Ammo (ammunition for a powerful weapon).

To the right of the red light room, there is a small room with an Small Medikit.

Open the next door, then quickly close it to avoid detonation by the Sentry Drone inside.

Follow the shaft downwards to its end.

A platform to your right holds Chaingun Cannon Ammo (ammunition for a rapid-fire weapon) and a switch.

Activate the switch to summon a cart.