Royal Observatory Greenwich
Straddle the courtyard line and you've got one foot in the eastern hemisphere, one in the western.
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Founded in 1675 as Britain's first purpose-built scientific research facility, this is where the Prime Meridian (0° longitude) and Greenwich Mean Time were fixed — on a hill in Greenwich Park overlooking the Thames.
What to look for
- The red Time Ball on Flamsteed House rises at 12:55, tops out at 12:58, and drops at 1pm — the signal that once let ships on the Thames set their clocks to GMT.
- John Harrison's four marine chronometers, H1 through H4, on display inside — H4 is the one that finally cracked longitude at sea.
- The meridian strip in the courtyard (originally brass, now stainless steel), plus the green laser fired north across London's night sky since December 1999.
Now a museum (since 1960), reached by an uphill walk through Greenwich Park; the Time Ball drops daily at 1pm, and a July 2024 renovation was announced to improve access.
Royal Observatory Greenwich is one of 40 sights worth the detour in London, all bundled offline in Voyage GO — download the London pack and it sits on your map with no signal, filling your travel passport the moment you walk past.
More to see in London
- British MuseumThe room where a dead language got its voice back — and you walk in for free.
- Buckingham PalaceThe balcony where a whole country turns up to watch a family wave — with 775 rooms behind it.
- Westminster AbbeyNearly every English monarch since 1066 has been crowned on the same worn patch of floor.
- Big BenThe clang in a thousand establishing shots comes from a cracked bell that's rung slightly off-key since 1859.
- Tower of LondonWilliam the Conqueror's keep turned royal prison, where two queens lost their heads and the Crown Jewels still sit under guard.
- Tower BridgeA Victorian drawbridge dressed as a Gothic castle, its roadway still splitting open for passing ships.