Margen
In the middle of the Bering Strait sit two islands almost touching: Big Diomede, Russian, and Little Diomede, American. Some 3.8 kilometres of water separate them — along with the International Date Line, which runs right between the two.
The consequence is wonderful: their clocks are twenty-one hours apart. That's why they're known as "Tomorrow Island" and "Yesterday Isle". From the American shore you can quite literally look at the next day.
In winter the sea freezes, and sometimes an ice bridge forms between them. Crossing it is forbidden — it's an international border — but the temptation is easy to understand: a twenty-minute walk would land you in tomorrow.
Time travel exists. It's just terribly cold.