San Sebastián and Donostia are the same name twice, Spanish and Basque, both meaning Saint Sebastian, and you'll see both on every sign. The city has fewer than 190,000 people and a story that nearly ended in 1813, when British and Portuguese troops who had come to drive out the French stormed it, burned it down and left one street standing. The walls came down in 1863, the new town went up in a Parisian grid, and from 1885 the widowed Queen María Cristina spent every summer here.
What you get today is a compact city around a bay with three beaches inside the urban area, a Parte Vieja where bar counters are covered in food, and green hills at both ends. Three days is the right length: two to see the city on foot, without rushing between a swim, a museum and the next pintxo, and one to leave for the coast. A fourth and fifth day add cider houses, Hondarribia and Pasaia, listed at the end.
Day one is the Parte Vieja, Monte Urgull and Gros, day two the bay from La Concha to Ondarreta and the top of Monte Igueldo, day three Getaria and Zarautz down the coast. Start on a Wednesday: San Telmo Museoa is closed Mondays, the markets Sundays, the Balenciaga Museum on Mondays for most of the year (and Tuesdays from November to March) and Elkano in Getaria on Sundays and Mondays. For the bigger picture, see Spain.