Situated to the west of Rhodes, Halki has been inhabited since antiquity, when it must have been very prosperous, judging from the coins found by archaeologists. Its name most probably reflects the copper ore (halkos) once mined there.

It is a small but mountainous island, just 28 square kilometres in area. The island capital and port is called Halki or Nimborio. Situated on the southeast coast, its two-storey houses with their tile roofs seem to climb up the sides of the hill overlooking the bay of the same name. In earlier times, the capital was at Horio, which was placed well inland, in an effort to escape the frequent pirate raids that were once the scourge of the Aegean. At its peak, it boasted 4,000 inhabitants; nowadays it is deserted. Its stone houses, built in tiers like an amphitheatre, are mute reminders of the past prosperity.

Above Horio, the ruined mediaeval castle occupies the site of the ancient acropolis. Within its walls is a church dedicated to St. Nicholas with frescoes. As there are no cars, buses or taxis on the island, you have to walk for about half an hour to reach Horio.