Secret Places (4)
In "One Eyed Pete's Shooting Gallery" you'll find a crack in the wall on the left side. Blow it up to find a secret place (watch out for the Protector Drone that flies out).
Still in the shooting gallery, shoot the second and fourth targets to open a "secret" place containing the red access card. You wouldn't be able to complete the level without finding this secret.
You'll come across this area during the "Babes of the Caribbean" boat ride. Beside the dog is a crack in the door. Blow it up to find another secret.
There really aren't any hints to assist in finding the last secret. Perhaps the figurehead on the front of the ship is supposed to draw attention, but she's not really pointing the right way. Use a jetpack and fly straight up above the figurehead, and move into the wall near the ceiling.
These combination switches are in the central lobby area, though they are somewhat hidden and require a bit of acrobatic skill to reach. You can find them by climbing the pile of boxes by the fountain, then jumping onto the ledge, and finally hopping across the fountain columns and into the crevice in the wall. Due to the way the switches are arranged (vertically stacked in pairs), the top right switch must be shot. The correct combination releases the blockade to "One Eyed Pete's Shooting Gallery" (left side of image). However, entrance to the gallery itself still requires the blue access card.
These combination switches are found in "The D-Cup Ride". There are three switches. You can activate them either by hand or by sitting in the cups and shooting at them, whichever you prefer. Activating all three unveils the blue access card within the column in the center of the pool.
These targets are found in "One Eyed Pete's Shooting Gallery". Shoot the second and fourth targets. The correct combination opens a "secret" place containing the red access card, as described in the secret place listing above.
These combination switches are found inside the "castle" near the end of the level. The castle itself is found by deviating from the thoroughly unexciting "Babes of the Caribbean" boat ride (I'm surprised they didn't make the boats pass through this area, it's entirely feasible). The correct combination opens the door.