Hammond Castle Museum, a mansion overlooking Gloucester Harbor, was built by inventor John Hammond Jr. Hammond, who was inspired by castles during his childhood in England.

AP / JOSH REYNOLDS

GLOUCESTER, Mass. — As eye-popping as the towers, turrets, and arches of this medieval castle plunked on a wooded lot in a residential neighborhood might be, nothing about the architecture of Hammond Castle can compete with the drop-dead-gorgeous ocean view.

Inventor John Hays Hammond Jr. (1888-1965) built the castle between 1926 and 1929 for his wife, Irene, and to house his collection of Roman, Renaissance, and medieval art and artifacts. The building also housed the Hammond Research Corp., from which Hammond produced some 400 patents and the ideas for more than 800 inventions. Second only to Thomas Alva Edison in number of patents,  Hammond’s is best known for the development of remote control using radio waves.

While the Hammonds entertained in the lavish dining room, courtyard, and Great Hall, their private apartment was three plain rooms, decorated in a traditional 1930s style, which are now used as museum offices. The castle was largely for show.

But what a show it is! Visitors enter the drawbridge room, with its grated window in the door, then descend a narrow, spiral stone staircase to the Great Hall.

This massive room is 28 feet wide and 100 feet long. Colorful banners hang from the 65-foot vaulted ceiling as dramatic medieval music plays. It houses some of Hammond’s most unusual pieces, including a stunning Buddhist manuscript case fashioned from pieces of colored mirror dating to the late 17th or early 18th century. The object said to be Hammond’s favorite is a skull given to him by the governor of Santo Domingo and purportedly belonging to a member of the exploring party led by Christopher Columbus.

The centerpiece is the 8,200-pipe Hammond organ, said to be the largest pipe organ ever installed in a private residence. (The inventor of the electric Hammond organ was Laurens Hammond, no relation to John.)

From the Great Hall, steps lead to a courtyard that captures the quintessential European feeling of indoor-outdoor space. Lush ferns and flowers surround a pool the Hammonds and guests used for swimming.

A round turret room that served as the library features a “whispering ceiling,” designed so that the slightest whisper carries across the room. It holds 1,500 of the estimated 4,000 books Hammond owned. A laviharp — a combination of harp, harpsichord, and piano made in the 1700s in Paris — dominates the space. A red door leads to the war room, another round room filled with medieval weapons, pieces of armor, and murals of sea battles.

From the Renaissance dining room with its intricate tiled floor and ceiling, you hear the trickle of water from the courtyard’s fountains and the roar of the ocean outside.

Upstairs, two bedrooms reflect different historical periods. The medieval Gothic bedroom, in shades of burgundy, features a stained glass window and 14th-century wrought iron bed. The early American bedroom, designed by Irene Hammond, has a secret passageway to the courtyard one floor below.

The inventions room showcases Hammond’s broad repertoire. A list of his patents includes light systems, eye wash, picture-reproducing apparatus, radio controls, orchestral controls, magnetic sound recording, insulators, containers, and cooking utensils.

Two industrial kitchens on the lowest level have opened this year for the first time, said curator John Pettibone. Visitors can see cooking equipment used in the Hammonds’ time. Servants’ quarters above the guest bedrooms have also been restored, affording visitors an Upstairs, Downstairs perspective, he said.

If gender permits, don’t leave the castle without visiting the ladies room overlooking the ocean. The vista may very well be the most spectacular view from a restroom you will ever encounter.