Ellie's crew has come across a rather amazing thing: a massive Necromorphic beast, frozen in one of Tau Volantis' facilities, which Ellie herself calls the Nexus. For some reason everyone thinks thawing this thing is a good idea. Far be it from Isaac to disagree. Now he has to get to the roof of the facility and get the heating working.
Check the recording in the Furnace Maintenance Room and keep going. In the Furnace Room itself you'll find a Suit Kiosk, and it in a brand spankin' new suit for Isaac: the Archaeologist Suit. Can't be a bad idea to switch, so don your new suit, check around the room for items (there's an Upgrade Circuit in a wall container) and hop on the lift. It will take you to the roof.
Check to the left of the elevator for a battery you can drag out of its node. This will alert Necromorphs ahead, which will assault you in waves of two. Despite being fast, strong and potentially ranged, these Necromorphs seem a little stupid, and won't come too close if you stick near the elevator. Strafe and fire to take them out. After they're gone, take the battery and wedge it through the half-opened door on the other side of the roof. Be careful not to fire it around - if you lose it over an edge you'll have to get another, and pulling a second battery from the node by the elevator will start the chain of Necromorphs again.
Go up the ladder to the catwalks. More Necromorphs will appear; murder them shooting gallery style. Go down the ladder at the end of the path, check the room over for items (such as an Upgrade Circuit in a wall container) and plug the battery into the glowing node. Activate the console beside it to get the heat running again inside. This will activate the door - and the noise will bring some Necromorphs into the room. Rather than turning to face the things, go for the ladder and climb out. They won't be able to follow. (You can even mock them from the lower portion of the roof. Just don't open the door.)
Return to the elevator. More Necromorphs will appear, but they're sluggish and can easily be ignored. Hop on the elevator and set it in motion to descend. One more awkward conversation with Ellie and Captain Norton later you'll be back inside. Return to the Nexus room.
The heat is on, but the enormous specimen isn't thawing. Isaac will have to adjust the pressure in the pipes at its base. This is a simple enough puzzle: just look for the lit pipe and use Kinesis on the wheel at its base. Keep doing this until the gauge in the middle reaches one hundred percent. Note that you have to let the wheel turn the full way around or it won't count. The heat exchangers will go to work once you hit the top and activate the console.
Run back to the Bench to find an elevator. Go up and you'll find Central Operations. One of the crew is waiting, and she'll give you blueprints for a Probe Gun that will allow you to properly examine the Nexus. You lack the proper pieces, though, so you'll have to head to another warehouse nearby and poke around for the parts you need. Sounds like a plan.
Go back down the elevator. Leave the warehouse and make your way back to where you fought the drill. You'll find a group of Unitologist goons… killing themselves? Weird… well, their loss. Leave the building, head back out onto the cliffs, and use the elevator to the right of where you come out. This will take you up to another part of the installation… and, yeah, the first thing you see is a fleeing Necromorph. It's going to be one of those kinds of trips.