Richard, Jack, Eloise and Sayid swim through to the tunnels

Richard Alpert is the first to jump into the creek and swim to the tunnels. Jack prepares to go under next. He tells Sayid that he won't blame him if he doesn't come. Eloise tells Jack to take a deep breath and that there will be an opening in the far end. We see Jack swim towards the small waterfall and under the rocks. He makes his way through a tunnel with and comes up in a chamber.

Jack tells Richard that it was a lot further than he though it was. He scans the room which has hieroglyphics on the columns. Jack asks "Where are we?" and Richard says "The tunnels." Jack asks how they're going to get a bomb out of here. Richard says "The same way we brought it in" and Jack replies "I assume you don't mean through the pool." Richard says "It's a 12-foot long, 40,000 pound hydrogen bomb. No, not through the pool."

Eloise comes up through the pool and Sayid is right behind her. Jack goes to help Sayid and says "I didn't think you'd come." Sayid says "Well, if this works, you might just save us all. And if it doesn't, at least you'll put us out of our misery." They then set off on their journey through the tunnels. Richard seems considerably less than thrilled about this entire situation.

So what exactly are the tunnels for? It seems possible that this is how the smoke monster travels through the island. Richard seems to go along with Eloise's plan even though he seems incredibly skeptical about the entire thing.