The Far Side Is Usually Ocean

A point directly opposite you on Earth is called your antipode. On a globe, find it by switching hemispheres—north becomes south—and moving halfway around the planet in longitude. Because ocean covers most of Earth’s surface, most antipodes fall in water. A tunnel continuing through the center would therefore usually emerge beneath the sea.

Why the Matchup Is So Lopsided

Continents occupy a smaller share of the globe than oceans, and their locations do not neatly mirror one another. Land opposite land is uncommon; land opposite ocean is much more typical. The result depends on the starting point: some places have land at their antipode, while many do not.

So the likely destination is not a particular country or landmark, but open ocean—possibly far below the surface. Your exact location would determine which stretch of sea lies on the other end.