The Caspian Sea is often called the world's largest lake because it has no outlet.

The longer version

A water body with no outlet to the ocean is called endorheic. Water leaves only by evaporation, so dissolved salts accumulate over time. The Caspian is called a lake by that definition, yet its size, depth and salty water make it behave like a sea in other respects, with waves and currents of its own.

Its level has fluctuated over history as inflow from rivers and evaporation shift with climate. Because the water is salty but less so than the ocean, it supports species found nowhere else. Legal classification has been debated, affecting fishing rights and resource claims among bordering states. Seals and sturgeon live in its waters.

Where this entry sits

These facts wander across maps, borders, deserts, rivers, mountains, and the extreme corners of the natural world. Each one is short and self-contained, offering a small surprise about places you may never visit rather than anything you actually need. The full list sits on the Geography page, where every entry is listed in order.