Eloise, Richard, Jack and Sayid reach Jughead in the tunnels

As they're making their way through the final tunnels before reaching Jughead, Sayid tells Jack that Eloise's motivation for detonating the bomb is likely that she just wants to annihilate the Dharma Initiative. Jack says he trusts her because 30 years from now she's who will help them get back to the island.

They reach a large room where Eloise uncovers Jughead. They all just stare at it for a moment and we can see the leak that Daniel pointed out previously is still there. Eloise breaks the silence by saying "Well... now what?"

What was this underground chamber's purpose when it was constructed? Presumably it wasn't always there so they could store a bomb in it. How exactly will they get the giant bomb out of there and how did the others get it in there?