5 Sights in London Borough of Hillingdon, United Kingdom (with Map and Images)

The Principal Triangulation of Britain was the first high-precision triangulation survey of the whole of Great Britain, carried out between 1791 and 1853 under the auspices of the Board of Ordnance. The aim of the survey was to establish precise geographical coordinates of almost 300 significant landmarks which could be used as the fixed points of local topographic surveys from which maps could be drawn. In addition there was a purely scientific aim in providing precise data for geodetic calculations such as the determination of the length of meridian arcs and the figure of the Earth. Such a survey had been proposed by William Roy (1726–1790) on his completion of the Anglo-French Survey but it was only after his death that the Board of Ordnance initiated the trigonometric survey, motivated by military considerations in a time of a threatened French invasion. Most of the work was carried out under the direction of Isaac Dalby, William Mudge and Thomas Frederick Colby, but the final synthesis and report (1858) was the work of Alexander Ross Clarke. The survey stood the test of time for a century, until the Retriangulation of Great Britain between 1935 and 1962.

Wikipedia: Principal Triangulation of Great Britain (EN)

Harmondsworth Great Barn is a medieval barn on the former Manor Farm in the village of Harmondsworth, in the London Borough of Hillingdon, England. It is north-west of fields and the A4 next to Heathrow Airport. Built in the early 15th century by Winchester College, it is the largest timber-framed building in England and is regarded as an outstanding example of medieval carpentry. It was described by the English poet John Betjeman as the "Cathedral of Middlesex". A similar though smaller barn is part of the Manor Farm complex in Ruislip.

Wikipedia: Harmondsworth Great Barn (EN), Website

The Polish Air Force Memorial is a war memorial in West London, England in memory of airmen from Poland who served in the Royal Air Force as part of the Polish contribution to World War II. Over 18,000 men and women served in the Polish squadrons of the RAF during the war, and over 2,000 died. The memorial marks the southern extremity of South Ruislip in the London Borough of Hillingdon, near RAF Northolt, where seven Polish-manned fighter squadrons were based at different times in the war.

Wikipedia: Polish Air Force Memorial (EN)

Lake Farm Country Park is an expanse of green belt land approximately 60 acres in size fringed by trees and the Grand Union Canal, situated in the south of Hayes in the London Borough of Hillingdon. Its formal status as a country park dates back to September 2002.

Wikipedia: Lake Farm Country Park (EN)

The Open Air Theatre, Barra Hall Park, Hayes is a purpose-built outdoor theatre with concrete-step seating for up to 180 people. Originally built in 1951, the structure fell into disrepair and was rebuilt in steel in 2005.

Wikipedia: Open Air Theatre, Barra Hall Park (EN)