Greenwich Royal Observatory

You'll find yourself standing on the most famous line in the world at this historic observatory, literally straddling the Prime Meridian where east meets west. Since 1675, this UNESCO World Heritage site has been the center of global timekeeping, and you can explore the fascinating history of navigation, astronomy, and Greenwich Mean Time. The Great Equatorial Telescope, Britain's largest refracting telescope, is genuinely impressive, and the planetarium shows are worth your time if you're curious about space.

The experience feels like stepping into scientific history. You can set your watch to the daily time ball drop at 1pm (a tradition since 1833), explore the meridian courtyard where tourists queue for photos with one foot in each hemisphere, and wander through galleries packed with maritime clocks, astrolabes, and astronomical instruments. The views from up here are spectacular - you'll see all of London spread out below, from Canary Wharf's towers to the Thames snaking through the city.

Honestly, at £16 for the observatory buildings, it's pricey for what amounts to a few hours of browsing. The grounds are free though, and you get those same stunning views plus the meridian line experience without paying. If you're passionate about astronomy or maritime history, the full ticket's worthwhile. Otherwise, enjoy the free bits and spend your money elsewhere in Greenwich.