With Europe’s borders temporarily closed to American travelers, the continent’s icons shine an even more inviting beacon than usual—if partly because of their inaccessibility. And few European attractions pop up more often on postcards and in Instagram posts than its castles.
But the best place for serious castle spotters may come as a surprise. It’s not France’s Loire or Germany’s Bavaria. The true epicenter is Wales, which features more castles per square mile than any other country in Europe.
From the northern mountains of Snowdonia to Swansea Bay in the south, castles that could have dropped out of Camelot shoot up everywhere. Why the density? Blame it partly on Wales’ history as a contested territory. Fighting over turf, the Normans, the native Welsh, and the English, led by expansionist Edward I, all erected epic fortresses in an explosion of castle building that dominated the 13th and 14th centuries.
The sheer number of Welsh castles is matched by their variety. “For a small country,” says historian Kate Roberts, “we have just about every type and form, including concentric castles with moated...