The Grand Cathedral is the final level of Serious Sam: The Second Encounter.
The Holy Grail was stolen from the Ice Castle, and so Sam must find it in the Grand Cathedral, where it is guarded by Mordekai the Summoner.
- From your starting position, turn right and blast a darker-colored section on the wall to reveal a Heart and Serious Damage.
- At the end of the second corridor, you can see Groovy Gregory hanging out from one of the windows of a tower. Shoot him to spawn a Serious Damage.
- In the middle of the third corridor, on the wall at the left, shoot a darker colored section of it to reveal a teleport to a secret pumpkin field. Watch out for Static Cannons placed there, and do not move out of the path if you don't want to spawn extremely small Cucurbitos.
- (HD-only)In the fifth corridor, on the right wall where Beheaded Kamikazes spawn, at the base of a pillar is a darker colored section. Shoot it with any weapon to reveal some secret items.
- In the sixth corridor, on the right side of the wall is another darker section. Blast it to reveal a teleport to an Embryo Museum. Picking up any power-ups there will spawn two Highlanders: one on the left and one on the right.
- At the end of the sixth corridor and at the start of the seventh and final one, at the tower on the left there is a Harpy mooning the player from a window. Shoot her with the Sniper Rifle to spawn an invulnerability power-up.
- In the final battle, after approximately 85-90 seconds, a small section on the right side of the wall will open, revealing a secret Heart.
- If the player's health is low enough and the player is too close to Mordekai The Summoner when he dies and explodes, the explosion will kill the player; the game will however still count as cleared with a sound of applause, with the Croteam Bigheads appearing to mourn the death of Sam.