What secret lab would that be? X-10? That's in Red Forest. It's down a tunnel in the compound at the top of the path that leads up, the path that enemies roll explosive barrels down toward you. You have to get into the compound and then the tunnel isn't too hard to spot.
The darkness must flow down the river of night's dreaming
jack00 posted... I'm talking about the one you're supposed to open with the decoder which you find in the secret stash in pripyat.
At a certain point in the Sarcophagus, you will go up a few floors in a stairwell, and in the door opening of the exit of the stairwell, there are like 15 Monolith soldiers waiting. After you kill them, you can either go left to the Wish Granter (which is something you won't want to do), or go right. If you go to the right and get around the corner, you will eventually spot a crack in the wall (I think it's on your left, but I'm not sure) with a ladder going upwards. Climb up the ladder, and in this room you will find the door that leads to the Secret Lab. Press F to use the decoder and wait 30 seconds while you hide from the Monolith troops that will spawn. There's also an Exoskeleton in this room, so you may want to take that with you.