Aix Cathedral stands on the highest ground in the old town, on the spot where the Roman forum once was. It grew over fifteen centuries, and you can read each one in the building. The octagonal baptistery to the right of the entrance still holds Roman columns; the central Romanesque nave is plain and heavy; the Gothic nave on the left is taller and more delicate; the whole thing is wrapped in a sixteenth-century facade.
Inside, ask one of the attendants to open the panels protecting the Burning Bush triptych — it is one of the great works of Provencal painting and only briefly on view. The cloister next door is small, planted with a single fig tree, and worth fifteen quiet minutes. Free entry, closed during services.