Getting to the Yellow Key Slot (5)

Jump into the rock path to the right of the Blue Key platform and follow it upwards.

Initially, you will face two Sentry Drones and two Commanders. Prioritize taking out the Sentry Drones first, then use the Shrink Ray on the Commanders.

Be aware that more Commanders will appear.

Collect the box of Shotgun Shells on the roof, but be prepared for heavy fire.

Across from your position is a hole in the wall containing Troopers, three Commanders, a Battlelord, and any Enforcers remaining on the roof of the lower building.

SECRET 3: Facing the building across from you, go to the far left of your current building and jump off onto a ledge on the wall. Here you will find a couple of Troopers and a Chaingun Cannon. Open the window of this building to reveal a room with a shelf containing Chaingun Cannon Ammo.

Lower Building: Jump onto the sign on your building to collect an Atomic Health. From this sign, you can jump onto a ledge of the building across from you.

Jump over this ledge to find Devastator Ammo. A door above the building you were just on will open, revealing a Battlelord and two Commanders.

Allow the Commanders to approach you, then shrink them. Use the newly acquired Devastator Ammo to defeat the Battlelord.

You can enter the room the enemies emerged from to find RPG Ammo and Devastator Ammo.

Proceed through the small arch to collect Pipebombs and RPG Ammo.

Another door will open on a rock face across from you, containing three Commanders. Use the Shrink Ray to eliminate them.

Explore the ledges of this building to find a Shrink Ray and an Atomic Health.

Return to the room where the Commanders emerged to find Night Vision Goggles. A hint for Secret 1 is present on the dark part of the wall.

SECRET 4: On the building near the Yellow Key door, a ledge leads to an Atomic Health. Behind this Atomic Health is a secret door that reveals a Jetpack.