The Newhaven Lookout stands on the cliffs at Newhaven in an area known as Castle Hill. Today it is a Local Nature Reserve (LNR) of 13.8 hectares but it was once the site of a hill fort dating to the Bronze Age. The early fort was largely destroyed in the building of the later fort built between 1867 and 1871 and visible today to the east of the lookout.
The LNR consists of mixed habitats. The hawthorn and blackthorn scrub on the north-facing slope provides cover for varied bird life. Hazel and ferns give a woodland look to this area. In front of the lookout is an area of maritime chalk grassland kept short by rabbits grazing and some management. Birds foot trefoil and thrift grow here and butterflies and moths fly throughout the summer.
Below Castle Hill the cliffs between Newhaven and Brighton, comprising layers of chalk, clay and flint, are a Site of Special Scientific Interest. This section is unique in Europe for the length of exposure and its stratigraphical completeness. The only other similar cliff is at the Lägerdorf–Kronsmoor quarries in Schleswig-Holstein, northern Germany, where there is another almost continuous section in this stratigraphical interval. Kittiwakes and fulmars nest on the cliffs which are interrupted by large slumps where the clay has collapsed following erosion.
The beach below the cliffs is made up of shingle deposited by long shore drift. Where tides and storms throw the shingle up the beach, ridges are formed, larger pebbles at the top of the beach and smaller at the water's edge. Above the tidal limit is an area of vegetated shingle where sea kale and horned poppy flower in the summer.
An accessible path has been built up the hill to an area just below the lookout where everyone can enjoy the stunning view across Seaford Bay. Benches have been installed at various places across the LNR.
Castle Hill is owned by Lewes District Council and volunteers provide work parties once a month to undertake practical work under the guidance of the Community Ranger. Two free car parks give access to Castle Hill and to Newhaven Fort.