Peru has a very long coastline along the Pacific Ocean. Fishermen go out at dawn and come back in the morning with fresh fish, and ceviche is the simplest, freshest way to enjoy them. In Peruvian fishing towns, ceviche is often eaten for lunch, never dinner - because you want the fish as fresh as possible.
The 'cooking' happens because of the lime juice. Lime is very acidic - sour and strong. When the acid touches the fish, it changes the soft, see-through flesh into firm, white flesh, just like heat would. No stove, no flame, no pan needed.
Peruvian ceviche always comes with three sidekicks: a slice of sweet potato (called camote), a pile of giant corn kernels (called choclo) and sometimes a few crispy toasted corn pieces. The sweet potato cools your mouth between bites; the corn adds crunch.
Ceviche is so important to Peruvian people that there is a National Day of Ceviche - 28 June - and the dish has been declared part of Peru's official cultural heritage. Every region of the country has its own version, and families argue happily about whose recipe is best.