The large, shingled mass of Castle Hill, once the summer home of the naturalist and marine biologist Alexander Agassiz, a Harvard professor, sits on its high bluff like an imposing gatehouse to the East Passage of Narragansett Bay. Although it has been somewhat changed in its present use as an inn, its engaged towers, ornate dormers, and bowed porches still present a picturesque ensemble with much original detailing intact. Some of the bracketing and stick-work around dormers, eaves, and entry canopy confirm this as a transitional design between the Stick Style of the 1870s and the somewhat simpler shingled structures of the next decade. Inside, the effect becomes complete, as the first floor is intact, with dark wood paneling, carved woodwork, and large fireplace—a typically grand, dark-toned ambience for such a prominent house and patron.