I've never been to America but I have stood on American soil.
In response to the murder of President John F Kennedy the people of Britain gave to America an acre of land, overlooking the river Thames at Runnymede. On this ground, granted to the USA in perpetuity, a garden was created, opened by the Queen in 1965.
The garden, designed by Geoffrey Jellicoe, is said to be inspired by Bunyan's Pilgrim's Progress, representing life as a journey. A cobbled pathway ascends pilgrim steps, leading to an inscribed block of Whitbed Portland stone.
Additional to the garden, since 1966 the Kennedy Memorial Trust has provided 12 scholarships annually for post graduate students to study at Harvard and MIT.
The site is more an example of themed landscape than garden, don't expect a show. I guess that won't matter if your motivation is thoughts of the man.