Serious sam first encounter levels
Related achievements Serious Sam: Classics: Revolution Opening the pit unlocks the "There used to be an alligator pit here" achievement. At the back of this platform should be some discoloured floor - hit it with 10 rockets and it will break open into an empty pit. Circle jump around the wall for an empty platform. Walk towards the back of the temple until you reach a wall.
At the very bottom of the room where the Croteam Heads are, there are some rockets. Touch it to release the "Croteam fans" ( Croteam Heads). When you walk down the ramp, turn right, you'll see a door in the hallway next to the ramp.