The Sionis Steel Mill
When you arrive the signal is a bit odd and can have you wandering around all over on the lower level -- but do not do that. Go high -- and when you do look for the chimney with the faces hanging from it -- you will spot it. Now grapnel up to the nearby walkway for a mini-CS with Alfred that has you conclude that this chimney is the only way in!
Don't worry - you will not have to avoid the burning coke furnace at the bottom on your own, as when you grapnel up to the chimney you get a brief CS of yourself entering and then you get control back with you standing on a wire conveniently stretched across for you to perch upon. Go ahead and glide forward and then land and look to the right.
Gaining Access to the Steel Mill
This is your first "slide" area -- basically you just run towards the low-section and then hold RT to slide under it. Then you continue along the loop climbing the blockages until you get to the furnace, and which point you need to cool off the metal here -- so follow the instructions on screen, turn on Detective Mode to highlight the hatch, then grapnel it and pull it open to unleash its water.
Your next path is an on-screen prompt-assisted one -- just follow around, use the rail, jump to the other rail, and blow up the floor to drop down. As you move away from where you landed put Detective Mode back on and look to the left, and you will see another round hatch cover -- grapnel that to reveal a Riddler Trophy -- then grapnel the Trophy to obtain it.
--== The Loading Bay ==--
After you get the trophy crouch to enter the Loading Bay area and use your Batarang to turn off the steam and move under the next area -- above you is a pair of thugs having a conversation so pause and listen to that. Turning Detective Mode on allows you to see the crowd whose conversation you can hear!
Follow the narrow passage here until you encounter Harely Quinn's voice again -- and unlock the Achievement "Chimney Sweep" (10 GS) for getting through here undetected.
Continue following the passage and it dips down and goes under the floor that the crowd was on above finally stopping at a set of live steam pipes -- ahead is a set of three valves that you need to use to turn off the steam -- but there is a trick to this... Aiming and throwing is not going to work, you have to do rapid throws (tapping L1) to get them fast enough.
Shutting Down the Steam
The point to this was not so you could get past the pipes near the valves, but rather to enter the tunnel back behind you -- follow the bright orange pipe that goes along the back wall through a narrow tunnel that was blocked by steam until you turned off the valves -- this leads to a wide section of grating with a bunch of the thugs standing near it. If you have not figured it out, this is where you pop up and kick some thug butt!
Start the show by doing a Takedown from below -- then get ready to rumble! Seriously... Kick their butts. Now.
Hey good job! The end of the fight marks a short exchange with Harley and a call to Alfred, followed by a quick map of the Steel Mill to consult. You have a new objective -- save the doctor -- so let's do that now!
Head towards the door marked "Death Ride" and enter -- inside this short hall you will be prompted to look at and then scan a pair of Trophies. Do that and they are then added to the map so that you can come back later and get them -- and from here on out IF you are collecting Trophies on this play-through you should scan ANY Trophies you are not able to get immediately for lack of the right tools so that you have a map marker for them for later. Once you have scanned both of them look at the map and you will see that they are now marked there -- good on ya! You do not have the right tool to get them, so knowing they are there for later is a good thing.