The address is: The Waterside, Clink Wharf, Clink Street, London SE1 9DG.
You'll find the entrance diagonally opposite Bill's restaurant, on Clink Street. The door is marked 'The Waterside' and is the big blue/grey door to the right of 'Clink Wharf' residential block.
Google maps: https://goo.gl/maps/E2kqioDbGPN11kNY8
What3words: https://what3words.com/stick.twigs.bells
Nearest car park: https://www.justpark.com/uk/parking/london/s/southwark-bridge-road-london-se1-9hh/#utm_source=gmb