Old Trois-Rivières is the part of the city that survived the great fire of 1908. The lanes around Rue des Ursulines keep 18th- and 19th-century houses, old convent walls, small museums, and a quieter feel than the busier downtown blocks nearby.
It is small, so do not rush it. The pleasure is in walking slowly, reading plaques, and noticing how the old French colonial street pattern still shapes this corner of the city.