I used to sail from the Blackwater Estuary in South East England. My boat was berthed at Bradwell on Sea, a small village with many interesting features, including a Roman fort, a chapel dating from 654 AD, a WW II airfield, a nuclear Power Station, and an innovative system of flood defence.
A favourite type of yachting expedition was exploring remote creeks, commonly known as "ditch crawling". I have sailed nearly all the navigable salt-water rivers, creeks and coastline from Great Yarmouth to Eastbourne and it is still possible to find attractive anchorages or to berth alongside a traditional quay. See the Bradwell Cruising Club website for details of events they organise in that area.
I now sail from Poole Harbour on the South Coast of England. My boat is moored at the Redclyffe Yacht Club on the river Frome just below Wareham.