Enter the big room after the lift. Shoot one of the demolition charges, it will break a hole in the wall. enter, and you got your secret.

Right out of the door to the open yard, there is a switch. Push it, the ramp will fold down. Behind it, a goodie.

After you went past the pool, inside on the right is two broken doors. Crawl under the right one, under the next, and there is a secret in the wrecked room.