Greenwich Royal Observatory, located in the east London area, about an hour from the city center by subway. After arriving at Greenwich Station, walk up the mountain in the direction of Greenwich Park. It takes about ten or twenty minutes to reach the Royal Observatory on the top of the mountain. There are famous landmarks of the original meridian, which defines the date and time of the world, very ceremonial, and there are ancient outdoor astronomical installations, clock museums, etc., where you can feel the concept of "time".