Mariestad's old town is the compact district around the cathedral, with cobbled lanes and wooden houses from mainly the 18th and 19th centuries. West Sweden's tourism board describes it as one of Sweden's best-preserved older town centres, which is not hard to believe once you leave the main square.
The pleasure is simple: walk slowly from the guest harbour up toward the cathedral, read the house plaques where you find them, and look into the small courtyards and workshops that keep the area from feeling like an open-air museum.