It's just after the bit where the gas mask dudes roll shit loads of barrels at you, and those spinny flying bastards are in a room jam packed full of exploding barrels.
I can't for the life of me figure out how to get through the bars on the left hand side.
I think it's something to do with that valve on the pipe, but buggered if I can get to it
If I recall correctly you need to jump down to that valve, turn it (which raises the water level) and then go back to the room with all the exploding barrels and crap and swim through a big pipe which will take you to the other side of that gate.
I hate the ravenholm part. too many poison zombies.
there's that one part when you're leaving the building (after turning off the electric fence) where the 2 poison headcrabs come out of nowhere in the doorway... those things scare the shit out of me...