Greenwich meridian is the start of how we calculate longitude. It may not sound important, but without that we won’t have time or your GPS would not work. This Greenwich is in London and I went there for a visit last month.
Its cool to see where the line begins. It’s marked on the floor (unfortunately there’s a stupid long queue just to take pictures of yourself standing on the line).
Anyway, its still a nice visit as there’s the planetarium, the nice view and nice cool buildings too.
And you can touch the oldest thing on earth!