Step outside and destroy every moving Strogg above and below you. There should be about 16 Icaruses, Gladiators and guards on the hard level.
Hop down to the cave on the lower right (the one with the lava in it) and shoot at the crack in the wall to uncover a secret.
DonΓÇÖt enter the entrance with the gate - itΓÇÖs locked and itΓÇÖs also a trap to drop you into lava. First, scour the area for Armor Shards, health, and ammo - youΓÇÖre going to need all three!
Start climbing the cliffs to find another way in. Pick up the Invulnerability power-up and health packs. Step on the button to unlock the door below on the other side of the lava trap.
Walk around the cliffs until youΓÇÖre directly above where you started the level and press the green button. A secret door has opened inside the chamber so crawl back in where you started to access the goodies.
Head back down and walk on the edges of the bridge over the lava trap and enter the door. Fight the Tank Commanders and Icaruses but be sure to gib them so the Medic (coming in behind you) wonΓÇÖt resurrect them. As you head down toward the doorway with the circle above the door, watch out for a bunch of black guards to appear out of the rock. When youΓÇÖve mowed them down, walk into the cove to pick up the health and grenades.
Before you enter this new area with the red carpet-esque walkway, turn back around and walk across the edges of the lava pit back at the first large area. Kill the Icaruses and climb up the mountain all the way around again until youΓÇÖre over the chamber and near the green button you pushed. If you climb up even higher to the right (when facing the button), there is an opening to enter a secret area. The will be a locked door there until you cross the lava pit and take on the Strogg. ThereΓÇÖs only one lousy health pack in here, after all that.
Enter back into the lava pit area, and down to the right into the doorway. Take on the three or four Tank Commanders and enter the hallway to the left, with the Combat Armor.
Climb the small set of stairs and enter the next room overlooking the water to destroy the many Icaruses and a Gladiator. Climb around the edges to collect the health packs and if you fall into the drink, take the platform back up again.
Besides the platform, there are two other places to explore underwater here. One smaller platform will elevate you to a room with guards and a Gladiator. A second Gladiator will break out of the wall as you reach for the health packs. This door leads to the Lower Palace (level 2) so donΓÇÖt enter here just yet.
Head back out to the water, collecting the Adrenaline and grenade from where the Gladiator broke out from along the way, and then turn right. Enter the pipe and follow it around until you see a broken grate. Shoot at it to enter and allow the turbines to push you up. You will not be able to swim down this way again.
Follow the pipe around to an open area and dive down to collect some ammo. Walk up the winding stairs and blow away all the guards and the Gladiator. When you reach the top, go straight to the end and enter the door to the left, kill the guards and shoot the glass to grab the data spinner. You must now find the communications laser data CD in the Upper Palace (level 3).
Before you leave this cove with the data spinner, shoot at the plate in the wall to the right of the data spinner and then walk in and step on the plate. Turn around and pick up the Adrenaline behind you and press the green button. This extends the bridge over the water the entire way.
Walk across the bridge to the end, take a left and kill the Icaruses. Jump on the pipe to get the health, then jump down onto the ledges to collect ammo and other health packs. Eventually, fall into the water and you are now in the pipe from which you came. DonΓÇÖt enter the turbine area with the green glow or youΓÇÖll have to walk up and around all over again. Instead, follow the pipe back out and emerge to an area with a force-field. Collect the Power Shield and drop down deeper, swim forward, and enter the small of the two platforms to your left. You must now visit the Lower Palace (level 2) first, before gaining access to the Upper Palace (level 3).
Once the red force-fields are de-activated, hop back down underwater from the pipe and pop your head up to uncover a few power-ups previously inaccessible.
Unit 8 Level 1: Secrets
Secret: 1 - The cave on the lower right has a cracked wall behind the lava. Shoot at it to uncover a secret area with a Power Shield.
Secret: 2 - Before you go across the bridge, hop back up the side of the mountain again and press the green button directly over the door where you first came out. This will open up a secret area on the inside of the cave so drop back and head back in for some power-ups.
Secret: 3 - After killing the Strogg on the other side of the bridge, go back out the way you came and climb around the mountain for the third and last time. Jump up over the door where you came in and enter the now-opened cave with a health pack in it.
Secret: 4 - Near where you grabbed the data spinner is a wall that opens when you shoot at it. Then step on the plate on the floor, turn around and press the green button. This extends the bridge outside this room.
Secret: 5 - Any time after de-activating the red force-fields, you can return back to Level 1 and snag the power-ups in the above-ground opening between the pipes.
