A Potomac cruise, which can take from a few days to a month or more, is well worth the investment. The river is very wide and deep almost to Washington and can accommodate 15-foot drafts and masts heights to 135 feet. The well-marked, deep channel alternately favors first one shore and then another as you head upstream. The lower Potomac’s surroundings are broad and flat, while cliffs and houses line the shore upriver, offering breathtaking views.  Popular stops include historic St. Mary's City, Colonial Beach, and Washington, D.C.