Enjoy two of londons great attractions with this stunning and flexible tour of the river thames with entrance to the world famous royal observatory in greenwich hop on and hop off your river sightseeing cruise from any of four conveniently located piers as many times as you like for 24 hours before discovering the past present and future wonders of astronomy at the royal observatory explore how great scientists first mapped the seas and the stars and then stand astride two hemispheres at t