Appropriately I'll start with Adam and Eve Mews in Kensington. Mews were originally built as a place of storage for horses and carriages. As the motor car became more popular they were converted to garages. Mews are usually only found in well to do areas of London as this one is.
These steps lead down to the River Thames in Wapping and are known as Alderman's Stairs. This was once a busy access point for passengers to board the ferry boats operated by the watermen.
This narrow entrance leads to Catherine Wheel Alley and it's opposite Liverpool Street Station on Bishopsgate. It's the narrowest alley I've yet to discover. It exits at the other end in to Middlesex Street, otherwise known as Petticoat Lane of flea market fame.
This large factory in Frederick Close (a mews) in Paddington was a musical instrument factory from the late Victorian period.
Below is a little house at the end of a cul-de-sac and tucked almost under a railway line in Putney. I can't decide if I'd like to live there or not!
Every time I enter a mews or an alley I feel as though I've stepped back in time and it's the closest I'll ever get to time travel.