St. Mary's City is not really a city now. It is the site of Maryland's first colonial capital, spread along the St. Marys River in southern Maryland, with a small college campus beside it and a large historic area where archaeologists have rebuilt pieces of the 17th-century settlement.
For travelers, the reason to come is Historic St. Mary's City. The museum combines active archaeology, reconstructed colonial buildings, a recreated Yaocomaco village, and the Maryland Dove, a working reconstruction of the ship that came with Maryland's first settlers. It is a quieter cousin to Jamestown and Williamsburg, but the story is just as important: early Maryland, religious toleration, plantation life, and the Chesapeake frontier.
St. Mary's City is best as a half-day or full-day stop if you are already exploring southern Maryland. The setting is calm, the river is beautiful, and the history feels close because the modern town never grew over the old one.