.io is one of the fastest-growing top-level domains on the internet, a particular favourite among start-ups and technology companies. It's also one of the most expensive. To the ear of the tech-savvy, “io” sounds like “input/output”, and it’s used for everything from business software and databases to bitcoin and blogs. But like all the other domains we’ve looked at, .io is also a place: a country-code top-level domain, or ccTLD, which refers to a particular place on the Earth's surface. In this case, that place is the British Indian Ocean Territory, a remote but strategically-important scattering of islands in the middle of the Indian Ocean, also known as the Chagos Archipelago.