On Michigan Ave and North Capitol St you’ll notice a string of cylindrical concrete structures that look like the entrance to the Kingdom of the Mole People sticking out of a grassy field. This is the McMillan Reservoir Sand Filtration Plant; the buildings are ruins of old water reservoirs. Since 1987 the huge property has sat empty while the District tried to decide what to do with it. Suggestions ranged from a new park to more housing.
In 2017 developers got a plan approved for both a new park and more housing, though it'll take several years to complete. In the meantime, those old reservoir towers look pretty cool from the road.