09:30, before the day's coach groups reach the piazza
Two chapels in one building carry most of what Siena has of Catherine, and they sit at opposite ends of the nave. Go up the steps at the entrance end first: that raised chapel belonged to the Mantellate, the lay Dominican women who wore the habit but lived in their own houses, and it is where Catherine was clothed as one of them in her teens. Andrea Vanni, who knew her, painted her there, and it is the only likeness made in her lifetime. Then walk the length of the nave to the chapel built in 1466 to receive the relic of her head. The reliquary niche beside it holds the relic of her thumb, the chalice she used, and the cords of her discipline. Sodoma frescoed the walls in 1526 with her collapsing and being held up, which is closer to what her contemporaries described than any calm altarpiece.
Whose lives these are Saint Catherine of Siena and Saint Dominic
Give your time to The Cappella delle Volte and the Vanni portrait before anything else, then the relic chapel. The nave is worth ten minutes as an argument about what Dominican churches were for, but the chapels are the reason to come.