Following the events of Serious Sam: The First Encounter, after Serious Sam defeats Ugh-Zan III, he goes aboard the Sirian spaceship, the SSS Centerprice and heads off to Sirius. Some Croteam Heads follow Sam's ship, riding on their crate bus. When Sam's spaceship gains speed, the Bigheads decide to use "hypercrate" to catch up with him, but suddenly, the brake to the crate bus stops working. The crate bus crashes on impact into Sam's spaceship, and it crash-lands in Central America, Sierra Madre de Chiapas. Sam must now find the second backup spaceship that was left by the Sirians. To do this, he must find the Time-Lock left to the Mayans by the Sirians. It is located in the grand Mayan city of Teotihuacan, so Sam must fight his way there.
From your starting position, dive into the lake, all the way down, until you see a rather bright spot with an XPML21 Rocket Launcher. Pick up the rocket launcher to register the secret.
Once you surface from the lake, turn right, you'll see some small terrain there, with a tree. Go there, and pick up the armor there to register the secret, although there's a Schofield .45 there as well, but doesn't count as a secret.
From #2, there's a phone booth near the corner of the terrain (behind the rocks, in Serious Sam HD ). Go near it to register the secret, and use it to make a phone call.
(Serious Sam HD only) cut down or blow up 3 trees in the starting area, before the temple, to spawn a Thompson submachine gun.
(Serious Sam HD only) cut down or blow up 3 more trees in the starting area, before the temple, to spawn some bullets.
(Serious Sam HD only) same as #5, to spawn more bullets. On higher difficulties, if you pick up both bullet pickups and the Thompson, two Highlander Aludran Reptiloids will spawn. One right of the temple, far away, and one a bit before the temple to the right, not that far.
From the temple's position, before entering, follow the wall to the left until you see some differently colored wall. Blast it with a rocket to reveal an entrance.
From #7, proceed through the entrance to discover a secret hall of fame, and stick around for a small speech and then disco music.
From #7 and #8, turn left and follow the path to the valley. You'll see some crates. Go near them to register a secret.
From #9, there's some rockets behind the crates. Pick it up, but if you do, some waves of Beheaded Kamikazes (or Kleers, on higher difficulties) will spawn when you're about to leave the valley.
In the corridor followed by the crushing blocks, before going through the blocks, when facing them, turn around, and walk to the dark area, then turn left once you're in a dead end. You'll find Mental's secret room, with a few jump pads with letters on them. If you jump on any pad that doesn't glow, spikes from the ceiling will lower and lower with every jump, until you're impaled and killed by them. Jump on the pad with the letter M first, then on the one with E, then on the one with N, T, A, L. (forms the word MENTAL). A wall opposite of where you entered from will move, revealing an Extra Large Health. You can jump on any jump pad after picking up the health.
When you exit the temple, look towards the pit, on its wall on the side you're on. You'll notice a small ledge sticking out, with a rocket launcher. Drop there and pick up the weapon. Jump on the lower ledge with the teleport to get back.
After crossing the pit, and grabbing the first official rocket launcher, you'll notice a rock on the wall to the left, sticking out. It's rather spherical. Blow it up to reveal a secret path.
From #13, follow the path underwater, and you'll find yourself near a bridge. Pass the bridge and pick up the secret super health.
Before entering the final temple and finishing the level, jump in the lake and dive in until you see a brighter spot with a Large Health. Watch out for the Reeban Electro-Fish that appear upon entering the lake.
Serious Sam HD: The Second Encounter
Find all 3 rocket launchers in Palenque - Sierra de Chiapas.
Finish the first level of The Second Encounter without jumping in at least normal difficulty.
In the beginning half of the level, until the player enters the temple after the starting valley, is used as a part for the Palenque Demo.
This level is split into Sierra de Chiappas and Catacombs in Serious Sam: Xbox. Catacombs has its own music when inside and outside. One of its fight tracks is used for Jump Over, the Serious Sam HD: The Second Encounter versus map. Catacombs also has a complete new area, a huge ramp, with strange gravity, where enemies charge in from behind the ramp and the player has to fight their way through. It also has some elements from the Palenque Demo.
Sam's phone call to "Blondie" in Las Vegas asking if he's ready to come out yet is a reference to Duke Nukem Forever.
The "crate bus" references the introduction which is missing from the HD port, where Sam's ship crashes because this vehicle, piloted by Croteam Heads, crashes into it. This is later added in Serious Sam Fusion. The craft itself is a joke at the expense of Croteam's CEO Roman Ribarić, who thought the English word "crate" meant "vehicle" during an interview with satirical website Old Man Murray in 2000.
In the secret, Croteam Heads are wearing halos in the classic version but not in the HD version.
Incident at the Arena·Senator Cicero's Villa·The Senator's Vineyards·Praetorian Camp (lost level) ·Via Aurelia·Opening the Aurelian Gates·The Forum Romanum (lost level) ·Temple of Neptune·The Forum of Trajan (lost level) ·Through the Servian Gates·Temple of Mars·Addressing the Senate (lost level) ·Emperor's Gardens·Caesar's Sanctum (lost level) ·Caesar's Palace·Touts at the Colosseum·Under the Colosseum·Showdown at the Arena·Splashdown in Xifengkou·The Monkeys of Juyongguan·Jiayuguan Fortress·The Silk Road (lost level) ·Dunhuang Oasis·Magao Caves·Cave of the Wickermen·The Gate of Supreme Harmony (lost level) ·The Three Halls of Harmony·Yuhuayuan - Imperial Garden·The Beast Beneath the Palace·A Chilly Reception·The Steam Tower (lost level) ·Temple of Steam·The Deep City·The Geothermal Tunnels (lost level) ·The Guardian Gates·Hall of Translation·The Tower of Confusion·Hall of Transposition·The Corridors of Power (lost level) ·Ascending the Throne·Sirian Mothership·Engine Core Critical·Gallery (lost level)
The Temple of Herkat Upper·The Temple of Herkat Lower·Amon Thule, Subterranean Palace of the Pharaohs·Slave Compound·Pyramid Entrance Maze·Tomb of Ramses·The Forum of Mars·Slave Quarters·Gladiator Training School·Baths of Diocletian·Preatorian Fort·Ceasar's Palace