The ruins of Longstone Manor lie on the banks of Burrator reservoir at the beginning of a small peninsula to which it gives its name, the Longstone peninsula. The site was abandoned in 1897 as a consequence of the construction of Burrator Reservoir which began in 1893. The house was in good repair at this time but after the site was abandoned the roof was removed and most of the east end stone walls were robbed out. The ruins have had some masonry consolidation carried out to stabilise the walls of the Manor under a successful bid for Heritage Lottery Funding.
According to Historic England the site of Longstone Manor house was owned from at least the 13th century by Herbert de Cumba, the then Lord of the Manor of Sheepstor. By the 15th century the Scudamore family owned the lands at Longstone, before they passed to the Elfords when John Elford married Johanna Scudmore. Much of the building, now in ruins, was re-built for Walter and Barbara Elford in 1633, according to a date stone removed from the ruins, possibly including elements from the earlier house. Their son, John Elford, is understood to have built the windstrew, a raised stone platform where corn was threshed by hand, to the north-west of the family farm in 1637 as well as a cider mill. The windstrew can still be found and there is a apple crusher in front of the ruins, a survivor from the cider mill. The date stone of the house inscribed with the year 1633 and other artifacts from the manor were removed in the early 20th century and are now situated near the Burrator Discovery Centre.