The only reason I gave this documentary a 9 and not a 10 is that I was left wanting more--more in depth coverage of the stories in the show. That's a good sign...and a sign you could possibly make a series out of this one.
This documentary is about all the different sorts of things that are mostly hidden underground in London and some were expected and some were complete surprises. Among the many topics quickly covered are the Black Plague mass graves, Roman walls, the Chiselhurst chalk caves, tunnels, buries rivers, the Cabinet War Room, silver vaults as well as portions of both the British Library and British Museum. It's wonderful, particularly, if you've been to the city and you recognize many of the locations they discuss. Well made, never dull and well worth your time.