The Castle of Rock is the 28th level in Serious Sam 2.
Serious Sam enters the Castle of Rock's gardens. It turns out that, in order to access the King's birthday party, he needs to find four of the greatest singles ever made. Thankfully for him, those singles and scattered throughout the Castle's gardens. He manages to pick them up while taking out the enemies Mental spawns in order to stop him.
With the four singles collected, Sam is allowed access to The King's birthday party. However, the last gate before the birthday celebration is locked. Near the gate is an Elvian old man being harassed by several Zombie Stockbrokers. Sam kills the Stockbrokers, then wipes out the reinforcements that teleport in. Grateful for Sam's help, the old man gives Sam a key to the final gate.
Sam finally manages to reach The King's birthday party, but before Sam can reach the Castle of Rock's gate, a legion of Mental's forces attack Sam in another attempt to prevent him from meeting The King. As usual, Sam kills all of them.
Soon after Sam wipes out all of the opposing forces, Cecil the dragon kidnaps the kingdom's princess. The King brings Sam to his throne room and the two strike up a deal; if Sam can rescue the princess, the King will give him the last Medallion piece. Sam agrees, and heads off to the floating islands high in Ellenier's sky.
1. From the starting point, go forward until you reach a large area with a bush in the center of it that has a coin in front of it. Pick up the coin, then go to the center of the bush maze (there's a fountain surrounded by Shell pickups where the center is) and look for Johnny Lee Gnarr, a Gnaar with a saxophone and a hat. Drop the coin into the hat, and he will start playing his saxophone. A few seconds later, a Treasure Bag will appear from his hat and a secret will be registered. Note that if you pick up, then drop the coin for a few seconds, it will disappear. However, it will reappear at it's original a few second to ensure that you can get the secret.
2. Go back to the starting point, but this time go right instead of forward. Follow the hedges until you're positioned so that a square-shaped hedge is to your left and you are facing the right part of the castle. Shoot the hedge, and it will be destroyed, revealing a Treasure Chest and a secret will be registered.
3. As soon as you enter the second part of the level, run to the well that's directly ahead of you. When you get close enough to it, a Treasure Bag will come from the well and a secret will be registered.