Lopud

This guide to Lopud's Franciscan monastery, in the Dubrovnik archipelago, opens with a building that looks like a plain whitewashed church from the harbor but reveals, close up, a monastery built for a siege. Founded in 1483, it later gained what may have been the first true pentagonal bastion in the old Republic's territory, along with a doubled main door, a balcony for dropping oil or resin on attackers, and small doors cut through the seaward wall into a hidden sea cave. The guide connects those defenses to Lopud's outsized wealth, its captains once sailing roughly a quarter of the Dubrovnik Republic's whole merchant fleet. Look for the five straight edges of that eastern bastion, still visible in the stonework today.