So here's what I remember (i think). Main plot Spike and Xander get sucked/pulled/pushed and or fall into a portal to another world/dimension. Where they end up is uninhabited by people (kind of desert island-y). Spike doesn't go poof in the sun, Xander doesn't age. And in the end even when their friends find them they choose to stay there.
I think this takes place season 5 or 6 cause I'm pretty sure part of the story takes place in the Magic Box.
Also I remember Xander building them a cabin to live in, and I think Xander gets hurt at some point and Spike's freaking out cause he doesn't wan't to be left all alone.
Any help finding this fic would be much appreciated. Thanks!