Marie Curie visited Poland often, sometimes alone and sometimes with her family. During one of her visits, she set up the Polish Radium Institute for the research of radiation, a sister institute to the one that she had set up in France.
During the opening ceremony in 1932, she commemorated the event by planting a small sycamore tree next to the institute. At the time, people did not think much of it, but over the years the tree grew to be a respectable 62 feet (19 meters) high.
About the source
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.