Kitron is the liqueur that Naxos makes and nobody else does. It is distilled from the leaves of the citron tree — a knobbly, thick-skinned citrus relative that thrives in the island's interior — and has been produced here commercially since the 1890s. The Vallindras distillery in Halki is the oldest and most traditional producer, still using copper pot stills and a family recipe that has changed minimally in four generations. A visit here is one of the more genuine things you can do on the island.
The distillery offers free tours and tastings during summer opening hours. You walk through the production rooms — the stills, the ageing barrels, the bottling area — and then try the three varieties. Green kitron is the strongest and most bitter, made from young leaves and unfiltered; it has a resinous, bergamot quality that takes some getting used to but grows on you. Yellow kitron is sweeter and more approachable. Clear kitron, the mildest, is the one most people buy. The tasting is genuinely educational rather than just a sales exercise; the staff are knowledgeable and unpressured about purchases.
Kitron doesn't travel as widely as it should because production is small and export limited. If you encounter it on the island, drink it. The standard serve is neat, slightly chilled, as a digestif. It also mixes well with soda water and a slice of lemon if you want something longer and more refreshing for a hot afternoon.
The distillery is in the heart of Halki village, easy to find. Opening hours are typically mid-morning to late afternoon in summer; call ahead or check locally outside peak season. Bottles are available to buy at island prices significantly below what you'd pay if you found kitron in an airport duty-free, which is rare anyway.