While not entirely necessary (Sarlat is pretty small) it was nice to have a walking tour of the city. We used sarlat-tourisme.com with a tour that started at the TI (email them about alternative times and private tours). A 1 hour tour wound us through the historical streets where our guide pointed out sites like the House of Etienne de la Boetie, Cathedral of St Sacerdos, the Rue de la Salamandre, Covered market, among other sites. It was a great orientation and a good amount of historical information. You can also opt to follow a nicely laid out walking tour in Rick Steves France book.