Commanding a terrific view from the hill in Greenwich Park, with the towers of Canary Wharf spread out in its lap, the Observatory is yet another creation of Christopher Wren (from 1675), and the place from which time zones emanate. Historically the Empire’s most important house for celestial observation, it houses significant relics of star-peeping, but since it began charging in 2011, the paid areas became a tourist trap. Most of the good stuff—marked on the map in red—is free, including a small Astronomy Centre and an exhibition on time. The only things admission get you is an unremarkable ceiling-projection planetarium and the bulk of the Flamsteed House by Wren, which includes a collection of clocks that cracked the mystery of measuring longitude, ushering the English Empire to worldwide dominance. Most people plunk down admission not because they care about those but to get access to the Meridian Courtyard. The Prime Meridian, located at precisely 0[dg] longitude (the equator is 0[dg] latitude), crosses through the grounds and interminable queues of coach tourists pay at least £7 to wait an hour for a silly Instagram moment of straddling the line with a foot in two hemispheres at once—but the dirty secret is they don’t have to. The line continues on the walkway north of the courtyard, where it’s free and there’s never a wait. In the old days, the red Time Ball fell precisely at 1pm daily so that the city could synchronize their clocks; it still rises at 12:55pm and drops 5 minutes later. You could set your watch by it, but technically, you already do.