During a trip to Europe in the early 1870s, Nichols was inspired by the architecture he encountered there, particularly the buildings constructed of native stone. He built the home--which was to be a summer home--using the rocks that were common to most New England fields, in part because of their longevity and in part to demonstrate their usefulness to local farmers. The walls of the home are four feet thick. Nichols named the home Winnekenni, which is an Algonquin word meaning very beautiful.
Because of his declining health, Nichols was forced to sell the estate to his cousin, William Webb, in 1885. Like Nichols, Webb used Winnekenni as a summer home for ten years, before selling it to the City of Haverhill in 1895.
Though a substantial portion of the castle's interior was destroyed by fire in 1969, the castle's exterior--clad in formidable New England rock--survived and has survived, just as Nichols predicted. Though the castle is not open to the public except for events, the surrounding park is open year-round for hiking, biking, or skiing.