Age of Empires II: Definitive Edition (PC) - Achievement - Tour d'Italie
Construct a Donjon and use it to train a Serjeant.
This achievement is quick to obtain and if playing through the campaign, can first be achieved on the first Hautevilles mission - Guiscard Arrives. Simply take your hero and move to the Norman Barons (Red) camp to the north-west, change the diplomatic state with Red to enemy, kill the units there and you will be rewarded with some Serjeants. These unique Sicilian units can construct a Donjon, which is basically something in between a tower and a Castle. Once you construct it, you can train Serjeants from them. Simply order your Serjeants to construct one and then order a Serjeant from it and the achievement will trigger.