Greenwich: Measuring the World

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Cutty Sark Gardens, Greenwich

Welcome to Greenwich - the hillside where the world agreed how to measure itself, and almost none of the agreement costs anything to see. Everything on this route solves from free public ground; you never need to buy a ticket to finish a clue. The route is flat, short, and closes on a scheduled event: a 190-year-old time signal that drops at one o'clock sharp, every day the wind allows. Start by around 10:45 and you'll be on the park lawn in time to watch it; start later and you'll still get every stop, just not the drop itself. After the flat six-stop core, there's an optional, free walk up the hill to two more stops and the line where the planet's longitude was fixed to zero - entirely optional, and it does not loop back down, so decide before you climb.