The Palace of the Popes (UNESCO, €12 with audioguide or €14 with HistoPad — recommended) is the absolute essential. Built in 1334-1370 under 7 popes, it's Europe's largest Gothic fortress (15,000 m²). Visit: Grand Audience, Saint-Jean Chapel (Matteo Giovannetti frescoes), Saint-Martial Chapel, Pope's Chamber, Ceremonial Staircase, Doms Terrace (panoramic view). 1h30-2h visit. Arrive at opening (9 am) to avoid crowds.
The Avignon Bridge (Pont Saint-Bénézet, 12th-13th century, UNESCO, €5) — famous through the song "Sur le pont d'Avignon, on y danse, on y danse". Interrupted medieval bridge: only 4 of the original 22 arches remain (the bridge was regularly destroyed by Rhône floods since the 17th century). Interesting audioguide on history and legend.
The intact ramparts (4 km around the historic city, among Europe's best preserved medieval, built under Pope Innocent VI in the 14th century) — free walk on foot or by bike. The Rocher des Doms (public garden atop a hill behind the Palace of the Popes, free) offers the free panoramic view over the Avignon Bridge, the Rhône and Villeneuve-lès-Avignon.
The Place de l'Horloge (city's lively heart, terraces, opera, theatre). The Rue des Teinturiers (14th-century canal and water wheels, bohemian atmosphere). The Calvet Museum (Fine Arts, 15th-20th century collection, free), the Petit Palais Museum (Italian primitive paintings 13th-15th, free), the Lambert Collection (contemporary art, €12).
The Avignon Festival (July, created in 1947): In (official programme, 40 shows in 35 venues including the Cour d'Honneur of the Palace of the Popes — book 6 months ahead) + Off (1,500 shows in 130 venues, fringe atmosphere). The city becomes the world capital of theatre for 22 days.
Nearby (day trips from Avignon): Pont du Gard (UNESCO, 25 min, 50 m high Roman aqueduct, €9.50), Orange (30 min, UNESCO Roman antique theatre), Arles (45 min, Roman arenas, Saint-Trophime, Alyscamps — all UNESCO; Van Gogh painted here), Châteauneuf-du-Pape (20 min, AOC vineyards, tastings in around ten estates), Les Baux-de-Provence (50 min, classified Most Beautiful Village, Carrières des Lumières immersive show), Saint-Rémy-de-Provence (30 min, Van Gogh at the Saint-Paul-de-Mausole asylum, Glanum Roman site), Camargue (1h, manades, bulls, pink flamingos).