Knapp's Castle, Mountain mansion ruins in Santa Ynez Mountains, US.

Knapp's Castle is the remains of a stone mansion set at about 2,900 feet elevation in the mountains above Santa Ynez Valley. The site consists of sandstone foundations, archways, and partial walls that frame views toward Lake Cachuma and the terrain beyond.

The mansion was built in 1916 by George Owen Knapp, a founder of Union Carbide, on his 160-acre mountain property as a luxury residence with an organ room and observatory. A forest fire destroyed the structure in 1940, just weeks after opera singer Lotte Lehmann had moved in, leaving only the sandstone walls and pillars that remain today.

The site is privately owned and, as of August 2020, closed to the public because of active construction, so the photographers who once gathered at the arches can no longer enter. The name comes from George Owen Knapp, who built the mansion here in 1916. The ruins stand on land that was part of his 160-acre parcel.

Knapp's Castle is on private land and, as of August 2020, closed to the public because of construction; there is no legal access to the ruins or the ridge-top site. Santa Barbara County halted the owner's 2011 work for lack of permits, and equipment stayed on site. Check current access status before planning any visit.

The 160-acre parcel was so remote when George Knapp bought it in 1916 that a new road had to be built to reach the site. In January 2011 the owner added a stone amphitheatre-style structure; Santa Barbara County halted the work for lack of permits, and the equipment stayed on site.