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 judge much of it, and but over the years the tree grew to be a respectable 19 meters high. Somewhere before that it was officially adopted by the institute and even a small sign was attached to it that says. 'Souvenir tree,planted on the day of the opening of the Radium Institute on may 29 1932, by Marie Sklodowska-Curie'. It is lovingly called 'Maria'The tree can be visited from Monday through Thursday during office hours after scheduling a visit to the park with the Maria Skłodowska-Curie Society.
Source: atlasobscura.com