Finding Your Forever by Bess McBride

Deep in the forests of Western Washington, near the majestic dormant volcano called Mount Rainier, lays a small town that exists only in history. Partially submerged by a lake and largely buried by mud, weeds, grass and trees, Kaskade is lost in time. Unable or unwilling to die its natural death, Kaskade comes to life over a hundred years into the future on the summer solstice, hoping to capture new life for the town.
Not everyone who is taken will stay in Kaskade. Most of them return to the future on the next summer solstice. Who will Kaskade take next? And will they stay?
Brother and sister Jefferson and Martha Lundrum have settled into life as a lifelong bachelor and spinster. Does Kaskade have other ideas for them?