Sant Francesc Xavier — usually just called San Francesc — is the administrative capital of Formentera, which gives you some sense of the island's scale. You can walk end to end in ten minutes. The central feature is the Església de Sant Francesc Xavier, a plain whitewashed church that was fortified in the 18th century to serve as a last refuge during pirate raids: its thick walls and lack of windows on the lower levels were not aesthetic choices. The interior is simple and cool, worth stepping into for a moment out of the sun.
On Sunday mornings (and some weekday mornings in high season) a craft market sets up in the square in front of the church. It is a genuine artisan market rather than a tourist-tat operation — local jewellers, fabric workers, and ceramic makers rather than imported souvenirs. The Museu Etnològic de Formentera is nearby, a small museum in a traditional farmhouse that documents the island's rural past with tools, furniture, and costume. It is the kind of place that takes 45 minutes and leaves you understanding the island better.