It's her lantern. Like that one you've got there. Have you tried walking very far from it? Hurts like hell. Might make you black out. I've heard if you get separated too far from it, you can die. Robin says there's always got to be a Keeper, since the lighthouse is where the tools for communicating with whoever's outside this town are, and the lighthouse has to stay lit. When the last Keeper died, she lit the light with her lantern, so there she stays.

[It's an incomplete explanation, obviously. What really is that lighthouse for? What's inside, and why do the spirits defend it and its keeper with such intense violence and desperation? The half-answers Robin gives just fill him with double the number of questions.]