The William R. Thorsen House, often referred to as the Thorsen House, is a historic residence in Berkeley, California. Built in 1909 for William and Caroline Thorsen, it is one of the last of four standing ultimate bungalows designed by Henry and Charles Greene of the renowned architectural firm Greene & Greene and the only one located in Northern California. Thorsen can be toured throughout the week on an informal basis; one can simply knock on the door to visit.