These giant white egg-shaped structures visible on the tip of Deer Island (which is not actually an island; it’s accessible by vehicle and on foot) is Boston’s wastewater treatment plant, the second-largest plant of this type in the country.

It was the needed puzzle piece in cleaning up Boston’s harbor and providing the recreation possibilities now available on the shores of the Harbor Islands. The harbor was once one of the dirtiest in the country and is now one of the cleanest.

The plant uses methane to power a steam turbine generator, as well as a hyrdroturbine pushed by discharged water, to produce power for the facility; the steam also creates heat that is used to warm the buildings. The park has trails and great views of the harbor, and interpretive signs near the plant explain the facility to visitors.