There is a secret room in In Part III, Level IV. Right from the start of the level when you are on the top of the parking lot, just before the first ramp leading down, there are some green barrels stacked up. If you jump on them, then onto the junction box next to them, you can then jump onto the roof. There is a discoloured panel which will fall when you shoot it. Drop down through the grate inside, then switch on the radio for a secret message from Remedy.