However, getting to this point:
- After arriving in Hephaestus, proceed as normal until you get to the main chamber (this is easily noted due to the numerous bodies attached to the wall) and grab the Grenade Launcher. Defend yourself from the Splicers and proceed to the Core.
- Proceed to the Upper Workshop and then to the Lower Workshop and follow the arrow to the crawlspace, pick up the Audio Diary to learn which parts are needed to lower Ryan's defenses.
- Wires can be obtained from Big Daddies, a few which you have already walked by, alive and dead.
Next you'll need Nitroglycerin, which is in Ky's Office (you ran past this a bit ago, those two turrets guard the entrance right outside the crawl space, and several electrified arrows inside). The Nitro is behind glass, and the button to open the case is on the far side of the desk. Pressing it triggers a turret to appear near the room entrance.
Lastly, Ionic Gel, the random small blue canisters you've likely seen around the Core and in the Workshop areas.
- Once all items are collected, return to the Lower Workshops and assemble the bomb.
- Follow the arrow to Geothermal, and defeat the Splicers while the elevator is made usable.
- Finish setting the bomb up and head back to the main chamber and enter. There will be a lot happening, but you can freely explore, you're not timed here.
Once you arrive in the huge room and Ryan goes on about how this is his Rapture and sets the self-destruct mechanism in place, head to the right side and up the stairs to find a duct you can crawl in.
- Once you get to Ryan, enjoy the fruit of your hard labor.