The rough-cut
stone castle-like main house is built around a main block with a
conical-roofed round tower. Porches and verandas project from many sides of the home to take advantage of the views of the river and mountains in the area. The roof is consistent red
slate, with
dormers of differing shapes and sizes scattered throughout. One
gable to the east uses dressed stone, in contrast with the rest of the building. A north wing with library and extra bedrooms were added later. Four interior
chimneys are within the mansion. There are several outbuildings and other structures on the original property that are included as
contributing resources. To the northeast, on the mountain's summit, is Woodsome Lodge, a rustic log cabin with its own views of the Highlands. The estate's
spring-fed wooden water tank is also nearby. A stone
arch bridge was added at the same time as the library wing. Stone was also used for a -story
gatehouse along the winding driveway leading up to the house from Cat Rock Road (
NY 403). Buildings that predate the estate are also included. A -story farmhouse known locally as Wing & Wing, built some years before it was expanded into a contemporary cottage in 1858, is near Route 9D on the open
meadows between the road and the hill. Also there is a barn-and-farmhouse complex, with nearby
shingled home, built by other landowners at the end of the 19th century. A small guest cottage was later built on a separate property. Another Osborn-estate–related property,
The Birches, is at the very corner of Routes 9D and 403. It was used by Osborn's sons after their weddings, and is listed separately on the National Register, but was not formally part of the estate. ==History==