A 6th-century monastic city founded by Saint Kevin in a glacial valley with two black lakes — Gleann Dá Loch in Irish, “Glen of the Two Lakes.” On the floor of it: a stone round tower 30 metres tall (one of Ireland’s finest), a roofless cathedral, six smaller churches, an ancient graveyard still in use, and a high cross carved from a single piece of granite.

By the 9th century Glendalough was one of Europe’s great monastic universities, copying classical and Christian texts at a moment when the rest of Europe had collapsed into the Dark Ages.

Pro tip: combine the monastic site with the Spinc and Glenealo Valley loop — a 9 km hiking trail that climbs above the upper lake for the area’s best views. The Wicklow Mountains National Park visitor centre at the start has free trail maps.