Russia and the United States are less than 4 km apart

The border between the world’s two great Cold War rivals is usually imagined as a vast ocean. In one place it is barely a swimmable channel. In the middle of the Bering Strait sit the two Diomede Islands, and at their closest points just 3.8 kilometers (2.4 miles) of frigid water separate them.

Big Diomede belongs to Russia; Little Diomede, a windswept speck of about 100 residents, belongs to the United States as part of Alaska. On a clear day, people on the American island can look across and see Russian soil—roughly the distance of a short bike ride.

What makes the gap surreal is the International Date Line, which threads precisely between them. Because the two islands fall on opposite sides of it, they are nearly a full calendar day apart. When it is afternoon on Little Diomede, it is already tomorrow on Big Diomede—earning them the nicknames “Tomorrow Island” and “Yesterday Island.”

Stand on Little Diomede, look west at Big Diomede, and you are quite literally looking into the future.

NASA’s Earth Observatory notes the islands sit on opposite sides of that boundary, while Russia’s Big Diomede lies only about 40 kilometers from mainland Alaska. In winter, the strait often freezes into an ice bridge spanning the two shores—meaning that for part of the year, you could in principle walk from one superpower to the other across less than four kilometers of sea ice.