Greenwich pictures. Greenwich, a district of London on the river Thames, is the site of the Royal Observatory which marks the prime meridian of longitude, and also of the 'First shop in the world', proudly displaying its longitude next to its name. Greenwich is also home to a beautiful park, some very old streets, the Royal Naval College (the famous symmetrial building on the waterfront), and a hilltop vantage point from where all this (plus the Isle of Dogs with Canary Wharf's skyscrapers) can be seen.