Porrentruy is the main town of the Ajoie, the flat agricultural plain in the far northwest of Switzerland that nudges up against the French border near Alsace. It is the second-largest town in the canton of Jura and has a relaxed, slightly French character — more bistro than Beizli, more Alsatian wine than Chasselas. The Château de Porrentruy dominates from its promontory above the old town, a late medieval bishop's residence with towers that still define the skyline.
The town was an important centre of the Prince-Bishops of Basel for centuries, and the old quarter has a compact dignity to it: eighteenth-century townhouses, a handsome fountain square, and the Jesuit church of St-Pierre. Porrentruy is also known for its dinosaur-era fossil sites — the Ajoie region has yielded some of the richest Late Jurassic finds in Europe, and the JURASSICA Museum documents the excavations. If you have any interest in paleontology, the area around Courtedoux is genuinely significant.
As a base, Porrentruy works well for exploring the northern Jura. The Gorges du Doubs are within easy reach to the north, and the old Roman road over the Raimeux pass takes you quickly back into the Bernese Jura. The town itself is quiet and unhurried — not the kind of place you'll find on most Swiss itineraries, but better for it.