Built first by the Portuguese in 1588, and then completed by the Dutch from 1649, it still has an almost timeless air.
This is one of my personal favourites, with the thick walls enclosing a delightfully mixed community of Hindus, Buddhists, Muslims and Christians all – mostly – living in perfect harmony. Its beauty lies mostly in its location, right on the coast, and these days it provides the stunning backdrop for the cliff-diving world series. It was important for rejecting advances from Venice which wanted to take it – but those 12-metre thick walls were simply impenetrable. It's a stunning feat of engineering as it took just three months to build. The fortress outside the western walls of the city, it will be immediately recognisable as a stand-in for TV's King's Landing. None, happily, was as vicious as Cersei Lannister. The town is traditionally known as the Town of the Queens, since many queens of Portugal used to regularly visit. The best vantage point to explore its many charms are on those walls, walking across the tops for splendid views of the cobbled streets, painted houses, churches and tiny shops. On a lofty hilltop, and encircled by 12th-century fortress walls, Óbidos is one of the most lovingly preserved medieval towns in Portugal. If the townsfolk decided to slam shut the gates, even Daenerys Targaryen's dragons might have trouble getting inside. Inside, there are churches, Gothic palaces and the 12th-century cathedral. Towering walls built between the 11th and 14th centuries stretch for 2½ kilometres around the town, studded by 90 fortified towers. One of the most stunning is at Ávila, in the south of the Castile and León region, which has the most complete fortified complex in Spain standing high on a hillside.
TV mega-hit Game of Thrones has single-handedly turned the world's great fortresses into some of the sexiest, and most thrilling, monuments tourists now scramble to visit.