This level features an unusual location in which the player can get trapped: Leave the building through the eastern blue door and follow the wall to your left to two medikits in front of a gray bar. There is a stalagmite or tree stump to your left with just enough distance to the wall to get behind from the left, but not enough to get out again.
After collecting the blue keycard, backtrack to the room with two blue doors. Take the northern door, and follow the hill upwards. Before it takes its final bend to the right, open the left wall for two imps (one on easy skill levels), a computer map and six health bonuses (sector 448).
Return to the room with two blue doors. Take the eastern door, and move directly ahead until you come to a wall behind a box of bullets. Open it, the room behind counts as a secret (sector 444). Ascend the stairs and walk along the cliff overlooking the main route through the map. Drop onto the lower cliff to find a soul sphere and four armor bonuses.
From the yellow skull key go west and drop down on the cliff with some imps and five armor bonuses on it. Open the wall behind the middle armor bonus for a berserk pack and yet eight more armor bonuses (sector 468).
Right after opening the yellow door and using the switch behind it to raise the bridge, run northwards over the nukage to the rocket launcher platform (in the northeast of the red pillar where the yellow skull key was on). From the platform's eastern edge look to the south, where you see a nukage pit with a red triangle in its southeast that is in fact a teleporter. Use it (or the other teleporter in the northwest of the nukage pit east of the bridge) to get to an otherwise unreachable cave (sector 76) with an imp, eight health bonuses and a switch.
Use the switch in secret #4 and to raise some stairs. Drop down to the ground and climb on the platform south of the bridge. Stop before crossing it. Turn to the west, and you will see two mounds increasing in size; beyond it, a gap and a series of stone steps on the other side you raised before by using the switch. Take a running jump, ascend the steps to the top (sector 374) and enter the nukage cave to find the megaarmor.
It is possible to fall behind the stalagmite just off the balcony that's near secret 1 (sector 77), however, the player must be hugging the right facing wall going out of the cave for this to happen.