The Gunnersbury "Small Mansion" is pretty big and overlooked a lake which might be restored. The outside of the mansion looks great, but on closer inspection the building is lacking maintenance and is in a dire state. On the right of the building is Princess Amelia’s Bathhouse and on the left is the Large Mansion.
Gunnersbury Park is a park in the Brentford ward of the London Borough of Hounslow, in west London. Purchased for the nation from the Rothschild family, it was opened to the public by Neville Chamberlain, then Minister of Health, on 21 May 1926. The park is currently jointly managed by Ealing and Hounslow borough councils. See here