The castle was designed and built by William Gillette (1853–1937), an American actor most famous for his portrayal of Sherlock Holmes on stage.

[8] Gillette originally planned to build his retirement home on Long Island until he discovered the cliffs of the Seven Sisters while traversing the Connecticut River in his houseboat, Aunt Polly.

[6] Construction was performed by the Porteus-Walker Company, a leading contracting and wood-working firm based in Hartford, Connecticut founded by Gillette's childhood friend, Robert Porteus.

[8] It has been described as being designed in a medieval gothic, or an "American fairy tale mixed with European flair"[2] style, or as "a weird blending of Victorian and Arts and Crafts".

[4] The 3-story-plus-tower,[8] 24-room, 14,000 sq ft home was built of wood, cement, and local Connecticut field stone, supported by a steel framework.

[8] Visitors, reportedly including Albert Einstein, Helen Hayes, and Charlie Chaplin,[2][3] could ride the railroad around the estate and speed along the 100-foot-plus cliffs of the Connecticut River.

[3] The grounds also contained a root cellar, walking paths with near-vertical steps, a two-story gable-ended vernacular dwelling for servants, a small period barn, stone-arch bridges, wooden trestles spanning up to 40 ft (12 m), and a fish pond.