(HD and VR only) In the yard before the Moon Pyramid, next to the structure with the statue that will shoot fireballs is a doorway with a statuette above it.
When you kill him, some sniper rifle bullets and health pills will appear. This will trigger a bouncing Beheaded Kamikaze that will bounce high in the air in the area you are (hint: his first bounce is near the exit, just look up and left from your current position). Destroy the bush or crouch past it and activate a switch.
(HD and VR only) In the building in front of the force field, on its left side is a bush.
After the force field, go behind the right house to find some cannonballs.
Walk up to the remains and turn left to find a secret Large Health.
In the part where the Kleers come in, when you're in a lower-height area with a mini-pyramid in the middle, a few Major Bio-mechanoids will come bursting through the walls of where you came front.
Do not kill him until the secret has been registered.
Opposite of #1, to discover a "suicidal plant" ( Beheaded Kamikaze).
When exiting the starting building, head for the lower right corner of the area to collect an Ammo Pack.
Sam must pass through the serpent yards to get to his main objective the Sun Pyramid, which is where the Time-Lock lies. Serpent Yards is the fourth level of Serious Sam: The Second Encounter, Serious Sam HD: The Second Encounter and Serious Sam VR: The Second Encounter, the seventeenth level of Serious Sam Classics: Revolution, and the nineteenth level of Serious Sam: Xbox.