09 The Power of the Underworld

1. Mini secret. Health (+25). When you leave the arrival area, turn right and head into the sandbox. In the top right corner you'll find the health
2. Secret. Health (+100). By the Temple of Horus (far left from the entrance) there's a Pyramid shaped tomb with the health on it's left column. To get onto it, you need to get onto the broken wall behind the Temple. From there you jump onto the broken pillar behind the temple. Climb onto the top of the temple and jump onto the top of the broken wall between the temple and the tomb. From there you can jump onto the tomb and get the health. Since the walls are destroyable, you might not be able to get to this one.
3. Secret. Armor (+10). Inside the Temple of Osiris (far right), you can jump into the alcove behind the statue.
See this video for secrets 1, 2 and 3:


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4. Secret. Ammo (electricity +50). Before heading down to the Khnum, turn around and look for some stairs down. At the bottom there's a collapsed piece of ceiling blocking a doorway. Crawl under it to find the ammo.
5. Secret. Ammo (rockets +10). From the ledge above the Khnum's thrown you jump onto the throne.
See this video for secrets 4 and 5:


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6. Secret. Armor (+50). When you arrive at the penultimate area (resupply area), you'll there's an armor on the column just left of the exit. Tear down the column to get the secret.
See this video for secret 6:


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7. Secret Vista Found. Sniper Rifle, Vista achievement. Once you've cleared out the area just before heading into the map's final confrontation, you need to pick up a secret key. When looking at the hole into the last area, you'll see that the wall has an exposed ledge, where the ceilings used to be. Follow that ledge counter clockwise and pick up the key on the other side of the area. Once you have the key, run back towards the entry. The huge wall with the gated off "doorway" has a gate that you can now unlock. Inside there's a ladder that leads to the top.
8. Secret. Ammo (devastator shells +20). In the final area. When you get in, turn right and find the ammo just around the corner.
9. Secret. Health (+25). From secret 8 you run straight ahead to the back of the area.
See this video for secrets 7, 8 and 9: