A waterfront mansion at 3799 Flamingo Road on Siesta Key has sold for $10.5 million—the key’s second-highest sale ever. Located on the north end of the island, the 1.4-acre property has more than 700 feet of water frontage on the bay, canal and lagoon and has been featured in in publications including Forbes, The New York Times,Elle Décor,Dwell and Mansion Global.