On a dune not far away, two freshly built, very large houses interrupt this near-primeval landscape in the midst of the Cape Cod National Seashore, a federally protected area established in 1961 to limit exactly that kind of development.

Nearby, a Modernist beach house built around the time of the park’s founding is almost hidden in the dunes. Small and brown, it sits lightly over the land, on stilts. But while new houses, some still covered in Tyvek insulation, sprout on privately owned land in the midst of the national seashore, this one, like dozens of others from the same era, has been taken over by the National Park Service, which administers the seashore, and it is now rapidly decaying.