The Nelson Dry Dock was built in 1707 and used for ship building until 1968. It was bought by the nearby hotel in 1988 and filled as a water feature and is one of the few surviving dry docks along the Thames.
YOU CANNOT ACCESS THE CACHE VIA THE HOTEL
There is no need to enter the hotel grounds. The cache can only be accessed via the foreshore at low tide. You can check tide times here.
The best place to access the cache is at Horn Stairs, located directly opposite Cuckold's Revenge and shown as a Waypoint. There is parking available near to the access point.