Collioure (27 km south, 30 minutes by car or train) is the unmissable excursion from Perpignan. The town is a small fishing port with a 13th-century royal castle directly on the waterfront, set against the dramatic red-rock backdrop of the Côte Vermeille where the Pyrenees run down to the sea. Matisse and Derain painted here in 1905, Picasso, Dufy, and others followed, and what they were working out became Fauvism. The town is genuinely touristy in July and August — the main street can be impassable — but go in the morning before the day-trippers arrive and it remains worth it. The local anchovy industry runs several shops selling the tinned and salted product; this is a legitimate regional food, not a souvenir gimmick.
Canet-Plage is the nearest beach (10 km east, bus line 1 from the centre, about 20 minutes), with a long sandy shore, a marina, and the facilities of a proper resort. It is functional rather than beautiful but does the job for a half-day by the sea. Further afield, the Route des Vins du Roussillon runs through the inland villages of Maury and Rivesaltes and south to Banyuls; several domaines offer visits and tastings, and this is a good way to spend an afternoon if wine is an interest. The Cathar castle circuit — Peyrepertuse, Quéribus, Puilaurens — lies 50-80 km north-west and deserves a full day for at least two castles; a car is essential.