What action did Martin Luther take to protest the selling of indulgences in Wittenberg?

Martin Luther famously protested against the selling of indulgences by nailing his Ninety-Five Theses to the door of the Castle Church in Wittenberg, Germany, on October 31, 1517. This act is considered the starting point of the Protestant Reformation. In his theses, Luther questioned the authority and efficacy of indulgences and called for a theological debate on the subject.