Serious Sam: The Second Encounter/Courtyards of Gilgamesh

Secrets

There are eleven or twelve secrets, depending on the version of the game. Expect some of them to be traps.

1. Exit the starting room, and follow the right-hand wall. This leads two two ledges which you can jump to receive an Extra Large Health, but move away as a Major Bio-mechanoid will appear.
2. The two pool yard has an ammo pack hidden behind the right-hand pool.
3. In the two pool yard, the left hand pool has a grate open towards the center and on the upper section. This leads to an ammo pack.
4. When swimming to head towards the next yard, the path branches into three. Taking the middle path leads to a secret room containing extra large health.
5. In the yard after the swimming section, there is a tower on the right hand side. Look at it from the yard's destination (with a sniper rifle) to see a bullseye target. Shoot it to break open a wall that contains supplies (including invincibility and serious damage).
6. On the wall opposite of the previous secret, there's a small darker section on the left. A rocket will reveal a secret don't push detonator. If you choose to push it, you get to fight a Highlander Aludran Reptiloid which spawns directly behind you. In HD: It's not visibly darker, but seems to be centered on the tower.
7. In the same yard, behind the building are some rockets. Taking them will bring secret mutated plant and friends - converting nearby trees into bio-mechanoids (1 major, 2 minor). Note that destroying the plants ahead of time negates the secret.
8. Once you get the winged lion and enter the building, enter the right-hand passage, and follow the route to the end. This leads to a secret extra large health. Picking it up and trying to leave will lower the floor and require you to fight enemies. Additionally, it will place a lava golem on the path back, and the doorway back to the center will have two kleers ambush you as you exit.
9. HD only. When you reach the corridor with a large number of combined enemies (after a ramp down and a spiked pit), the first pillar has a small jumpable ledge. Additional ledges are present on the walls which you can use to reach a Large Health.
10. After the corridor, secret armor on the left.
11. When riding the platform at the "leap of faith" in the foggy abyss, there's a extra large health on the left. Shoot the support with a rocket to have it fall. It's centered on the platform when Sam says "Now I'm seriously serious" - if you wait any longer, you'll miss the health.
12. In the final courtyard (after getting the cannon), there's a bullseye on one of the towers on the left. Shoot it, and it will launch a few health power-ups into the air. The third one will land in the middle of the courtyard.

Level-skip glitches

• In the classic version, head towards Secret #1, and collect the extra large health. Wait for the biomechanoid to spawn, and use it's rocket to jump over the ledge, and go over the outer wall. Walk to the end of the level where you see a large extra health - activate the final secret with a rocket, and wait for the secret to launch you and the heart into the arena - this teleports to where you're expected to be, inside the arena grounds.
• In the HD version, head to the two-pool area. On the far tree on the right, fire two rockets to damage it, and jump onto it using the crystal decoration. If you jump onto it at the right angle, you can object boost across the map and reach the final courtyard. This glitch requires disabling V-Sync, and having a framerate of at least 200 FPS.