This is undoubtedly ‘Mecca’ to any serious horologists: the Royal Observatory Greenwich.
It is the home of John Harrison’s marine clocks, generally regarded as the most important time pieces ever made! Four of his masterpieces are on display here: H1, H2, H3, and H4. (H5 is at the Worshipful Company of Clockmakers at Guild Hall.) The museum does not allow photography so I have included publicity photos of each timepiece.
Greenwich Mean Time
Greenwich is the location of the Prime Meridian. The Prime Meridian is the meridian (line of longitude) at which longitude is defined to be 0°.