Greenwich: Measuring the World

Greenwich is where the world agreed how to measure itself, and almost none of the agreement is behind a ticket barrier. Eight stops from a dry-docked tea clipper to the line where the planet's longitude was set to zero: a ship that raced a rival home from China, a tunnel dug under the river for dockworkers who couldn't afford a ferryman, a naval college split in two to protect a view, a museum built around the problem that killed sailors for centuries, a house that is a perfect cube, and a red ball on a hill that still drops at one o'clock, every day the wind allows. The flat six-stop core is under a kilometre on level riverside and park paths - about 1 hour 45 minutes brisk, or 2.5 to 3 hours with a proper museum visit - and it ends with a scheduled spectacle: start by 10:45 and you'll be on the park lawn at 12:55 to watch it happen; start later and you'll still get every stop, just not the drop itself. An optional, entirely free uphill extension adds two more stops and roughly an hour. Everything on this route is solvable from free public ground.