Bernard Berenson’s home, the Villa I Tatti was bequested to Harvard University and is now The Harvard University Center for Italian Renaissance Studies. Scholars can arrange to study (Belle’s letters cannot be photocopied and must be studied on the premises) and travelers can arrange a tour of the buildings and grounds.
Villa I Tatti

The Pierpont Morgan Library (now the Morgan Library and Museum) has a detailed website of their new building and ongoing exhibitions.
Morgan Library

If you are particularly interested in the illuminated manuscripts whose brilliant artistry, historical significance, and cultural insights captivated Belle Greene and became the focus of her career, selected samples of pages from some of the Morgan’s holdings can be found here.
Some Morgan Library holdings