Concierge.com's insider take:
Greenwich is a bustling little market town in its own right, colored by bucketfuls of maritime history. Most importantly, it's where time begins. No, seriously, it does: At the top of a hill in Greenwich Park, a brass line marks longitude 0 degrees, the starting point of every time zone in the world—better known as GMT (Greenwich Mean, or Meridian, Time). The Royal Greenwich Observatory is up there, too, and for the effort of walking up a gentle hill, you'll be rewarded with excellent views. Down below are architectural gems: Georgian houses, the National Maritime Museum—designed by Inigo Jones, it displays Admiral Nelson's coat from Trafalgar, complete with the fatal bullet hole in the left shoulder (44-20-8858-4422; www.nmm.ac.uk)—as well as the stunning University of Greenwich and Trinity College of Music, designed by Sir Christopher Wren. The Cutty Sark, the last clipper ship to be built (dating back to 1869), has rested in a dry dock in Greenwich since 1954 and is currently being restored. Until it's completed in Spring 2010, you can only view the ship from the nearby souvenir shop; see the website for more details (44-20-8858-2698; www.cuttysark.org.uk). Nearby is the glazed cupola entrance to the Greenwich Foot Tunnel, which runs under the Thames. Alternatively, in keeping with Greenwich's nautical roots, catch a boat back up the river to central London.