Royal Sewers is the 26h level in Serious Sam 2.
After getting inside the sewers, Serious Sam finds a weak point inside the sewers that'd let him progress deepter into the sewers, and thus get closer to the Castle of Rock. Thankfully for Sam, someone left a TNT bundle nearby, which he uses to blow through the weak point. Passing through the weak point, he finds that he appears to be in the castle's mausoleum.
Sam travels through the sewers while destroying any resistance in his way. After traveling through a few tunnels, he enters a medium-sized room and finds two Orc Grunts harassing a Elvian woman. Sam kills them to save the woman, then wipes out Kleer Skeleton and Zombie Stockbroker reinforcements.
With the woman safe, Sam continues traveling through the sewers/mausoleum. Eventually, he comes upon a huge room with a golden statue of The King in the center of it. Apparently, the statue is required to open the exit to the Castle of Rock's gardens. However, once Sam grabs the statue, many enemies appear in order to kill him. As usual, Sam wipes them out. He then uses the statue to exit the level.
1. In the room where you have to save the girl from the two Orc Grunts, kill everyone in the room, then go back to where you entered the area. Now, look to your right and follow the path you see. You'll reach a door with two Orc Grunts walking around behind it. Kill them, and the door will open. Follow the path until you reach a gay wedding between an Orc Commander and a Zombie Stockbroker, a Gnaar in a priest getup, and with some regular Orc Grunts and Zombie Stockbrokers. Behind the two life partners-to-be is a Treasure Chest. Getting close to the wedding will register the secret.