Visitors approaching Singer Castle's South Boat House immediately see the castle's five-story Clock Tower. The granite tower and connecting bridge were built at the time of the castle's construction and Marjorie Bourne Thayer added the four-sided wrought iron faced clock, along with the fifth floor, to the tower during renovations in the 1920s. The tower has a winding staircase with sixty-two steps, six small landings and six large landings from its base to the clock works at the top. Frederick Bourne equipped the tower with a pulley system so that servants could life heavy items and guests' luggage from the tower base at the South Boathouse to the bridge that connected to the main part of the castle and the secret passageways used by the castle staff.

The tower clock, designed by the E. Howard Clock Company, has electric self-regulating clock works and Westminster Chimes that ring on the hour, the quarter hour and half hour and is valued at over $75,000. When it was first installed the tower clock operated on Dark Island's old direct current power system produced by the generator in the North Boathouse. After purchasing the Island in 1965 Dr. Harold Martin had electric power brought to the island from the mainland and converted the clock to accept alternating current. A similar E. Howard tower clock is in the collection of the National Association of Watch and Clock Collectors Museum in Columbia, PA.