The Observatory was built in 1809 by C F Grenville and is a Grade II Listed Building. It is octagonal in plan, constructed of stone and brick and has vaulted top with slit openings for the telescope at 10m (30ft) high. There are single story buildings on three sides used for classrooms and accommodation. The observatory is marked on an historic chart and was used as a navigation aid by vessels using the Haven.

Sources include:
Application for demolition public enquiry M/DES file 14/5/71
Historic Admiralty Chart 1410_A1, RCAHMW digital collections sourced from the UK Hydrographic Office and published in 1842
OS495card; SM80NE29

Maritime Office, RCAHMW, September 2011.