Which historic fortress sits atop Castle Rock, an extinct volcano in Scotland?

Edinburgh Castle is the historic fortress that sits atop Castle Rock, an extinct volcanic plug in Scotland.

Castle Rock formed roughly 350 million years ago, when molten rock cooled inside a volcanic pipe. The surrounding softer sedimentary rock was later worn away by glaciers, leaving the hard dolerite crag that made the site naturally defensible. Its steep cliffs meant that the easiest approach was from the east, along Edinburgh’s Old Town.

A royal castle has occupied the rock since at least the reign of Malcolm III in the 11th century. Edinburgh Castle remained a royal residence until the 17th century, after which it increasingly served as a military garrison, fortress, prison, arsenal, and treasury. It also houses the Honours of Scotland, the nation’s historic crown jewels.

The castle is sometimes confused with Stirling Castle, another major Scottish royal fortress, or Balmoral Castle, the royal family’s Highland residence. The key clue here is Castle Rock: it points specifically to Edinburgh Castle.