Located in a beautiful park, offering some of the best views over London, and the chance to straddle two international time zones makes The Royal Observatory, all puns aside, Greenwich's star attraction.
2009 is the International Year of Astronomy, but the first notion of a Royal Observatory was conceived in 1675, when King Charles II demanded a comprehensive chart made of the skies to aid sailors' navigation. £500 was alloted to the building and a measly £100 annual salary to the first Astronomer Royal, Sir John Flamsteed; he even had to buy his own telescope!
The Octagon Room was designed by Sir Christopher Wren (of St Paul's Cathedral fame) and was the intended site for the Meridian line to cross. However, despite his experience, he failed to get one major feature right: the position of the windows. As a result, Flamsteed had to relocate his telescope to the shed in his garden!
Over the centuries, Flamsteed's successors, gifted with better telescopes and more modern astronomical equipment, made increasingly accurate charts of the night sky and the famous 0 degrees Meridian line moved ever eastward. It's current location is where it was finally set in 1880. As well as sailors, the Prime Meridian is now also essential for pilots and, fittingly, astronauts.
Also in the Observatory, you'll find an extensive collection of time-keeping devices (from pendulum- and quartz-powered clocks to a Mickey Mouse watch (made famous in the 'Da Vinci Code' novel series). Make sure you read the interesting story of the red ball on top of the Observatory and the alleged origins of the expression 'keep your eye on the ball'. Don't miss the camera obscura (translated as 'darkened chamber') just off the courtyard. It contains a pinhole scope which projects an upside-down image of the view onto a white surface. Dark rooms such as this were the inspiration for the modern camera.
For the more technologically-minded, head to the Astronomy Centre also located on the site. Here you can play with a lot of interactive displays, study a selection of space photography and even catch a stunning 360-degree space simulation in the planetarium.