Disused fort on River Thames up for sale
13 August 2014 Last updated at 14:17 BST
A seven-bedroom mansion, with sea views and in commuting distance of central London, is on the market for £500,000.
This might sound like a bargain, but there are a few drawbacks.
You can only get to No 1 The Thames when the tide is low or if you have a boat as it is situated in the Thames Estuary.
BBC London's Gareth Furby took a tour with estate agent Nigel Day and spoke to its current owner Simon Cooper, from Eltham, south-east London.