Bill Gates - who we seem to keep coming back to in this list - didn't found Microsoft alone. His partner in the endeavor was Paul Allen, who was also set up for life financially when the company became a success. Allen is sadly no longer with us, but he used to own a slice of paradise off the coast of Seattle. There was nothing there when he bought it, but by the time he sold it for $8m in 2013 he'd had a lot of work done.
The island's new owner picked up a ready-made island retreat which featured an airstrip for private planes to come and go, a log cabin, a luxury home, and an electricity generator. It's completely self-sufficient, and boasts incredible views of the Seattle coastline. Thanks to Allen's vision, this rough diamond is now fully polished.