Occupy two different hemispheres at the same time on a family adventure to the Greenwich Royal Observatory, where you and your kids can pose for pictures as you bridge east and west with your legs. This historic spot in central London offers a fascinating look at how we make sense of the earth, marking the spot where British scientists established the Prime Meridien—zero degrees longitude—back in 1851. Scan the skyline for the brownstone Fleming Building topped with a bright red “time ball”—one of the world’s earliest public time signals—to find your way to the Meridian Courtyard. As you pass the 24-hour clock at the entrance, you’ll notice a thin metal strip running through the cobblestones in a straight line. This understated accent denotes the place where the hemispheres meet, split right down the middle of the massive telescope that occupies the royal observatory room. With the required goofy photos out of the way, head inside for a look at Greenwich’s long history of time keeping, moving from simple sundials and ornate golden astrolabes to intricate clocks and time-measurement devices, some of which still happily tick away inside of their cases. You’ll need to keep track of the time as you tour the compound so you can head back to the courtyard by five minutes to one. At precisely one o’clock Greenwich Mean Time, that red time ball quickly falls from its apex, signaling the exact time to boaters on the Thames. While there are plenty of ways to check the correct time these days, time balls like this one were once crucial tools used by navigators to verify their marine chronometers from their ships offshore. No, it’s not quite the Times Square ball drop on New Year’s Eve, but this temporal treat is just one of the fun reminders of the importance of this site, which still dictates the way we measure our days.