When you enter this level, you land - a bit rough - in front of this stained glass window. Shoot it, and a knife switch appears (for a moment) under it. Push the switch, and the cages behind you opens. One is the actual secret, the other a mere goodie.

Out of the room, to the right. At the end of the corridor, the footpanel is missing. Shoot here - it's a hidden door. Goodies inside. Don't run outside yet, wait until the door shuts again.

When the secret #2 door opens, it glides into a recess in the wall. When it's shut, you can enter the recess. Push the knife switch there, get out of the hole and shoot the door to open it again. Outside the door a hole has opened in the floor. It just looks like a goodie, but it will teleport you to the big wooden beams in front of secret #1.

Acrobatics time. You really should have stayed home on the farm, right? Well, you probably got dizzy rotating the crops anyway...

Just get on top of these beams, and inside the hole in the wall. You can jump right down on the top of the secret from there.

Haul your sorry ass up on those beams again, jump over to the platform in front of the stained glass window, and shoot the window. It opens. Jump into the hole. A lift (Luxury! When i was your age...) will bring you up to this concealed chamber.

Push the knife switch, and move swiftly away. If you aren't gone, when the grating retracts into the wall, you'll land in front of a Death Knight + some assorted trouble.

Assuming you did move, shoot the differently textured bit of wall at the back of the room. Then you have the drop on the bad guys. When you jump down here, the secret counts.