Like the cold, clear waters of Flathead Lake, mystique surrounds Cromwell Island. It overlooks the legendary Wild Horse Island, where Salish and Kootenai historically swam their horses to keep them safe from rival tribes. In the 1930s, construction started on a dam near Polson, Montana, at the outlet of the Flathead River. Prior to its completion, in periods of low water, Cromwell Island became a peninsula connected to the shore. It is all but certain that the Native Americans historically herded their horses onto this peninsula before swimming them across to Wild Horse. Today, Cromwell Island is a full-time island, the entirety of which is now for sale. Flathead Lake, with almost 200 square miles of surface area and 185 miles of shoreline, is the largest natural freshwater lake west of the Mississippi River — Yes, even bigger than Lake Tahoe! To our knowledge, Cromwell Island, with almost 350 acres and nearly three miles of shoreline, is the largest private island in freshwater west of the Mississippi River that is under a single ownership. Like Loch Ness, Flathead even has its own monster. While the lore of a huge antlered monster living in the lake is rooted in the ancient oral histories of the Kootenai Tribe, recorded sightings of the creature date back to 1889 when a steamboat captain along with 100 passengers spotted a “whale-like” object on the water that dove after being shot at by one of the passengers. Somewhere along the way, locals dubbed the monster “Flessie”, an obvious “hat tip” to her counterpart in Scotland. Cromwell Island was purchased in the late 1980s by Robert M. Lee, a renowned automobile and antique arms collector, explorer, author, and conservationist. Before his death in 2016, Mr. Lee and his wife, Anne, partially completed construction of a monumental structure including over 45,000 square feet of living space that was to serve as their home full-time. Even in its unfinished state, it has a magnitude of presence reminiscent of Versailles. The mystique endures as Cromwell Island is now for sale and, with so many possibilities, a new owner will have the opportunity to write the next chapter of a storied place.