Remember back to the speech Isabelle told Jack about how they only work on that island (they didn't really like coming there) And when Ben took Sawyer (when sawyer had that heart monitor thing) and hiked up to the edge of the island and showed him the Losties island across the water. I think there are two separate islands and the hydra station was on one and the Barracks are on another.

ALTHOUGH>>>> now that I think back to one of Marvin Candle's filmstrips he does say something about taking the Pala Ferry back to the barracks.... hmmmm.... now I have to research this.

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`Dear, dear! How queer everything is to-day! And yesterday things went on just as usual. I wonder if I've been changed in the night? Let me think: was I the same when I got up this morning? I almost think I can remember feeling a little different. But if I'm not the same, the next question is, Who in the world am I? Ah, that's the great puzzle!'

-- Alice, from “Alice’s Adventure’s in Wonderland”