I'm from London originally but probably only started discovering things about it as I grew older and more involved with my own direction of things to do - post university I'd say. (I didn't go to university in London.)
Whenever I discover something interesting to visit/see in London, I make a note in my diary and the next time I'm in the area, I'll seek it out.
One of such random things on my to do list was Lower Robert Street - a secret little road between the Strand and Embankment used mostly by Black Cabs.
It's pretty bizarre, part tunnel, part warehouse. To read more about it, visit here.
I then took my wanderings through Lamb & Flag Passage on the way to my dinner that night, a tiny alley that is almost part of the historic pub (Lamb & Flag).
All photos my own.