As part of her MFA, Alexis Lloyd created this very cool site, My Washington Square, which gives people a way to share experiences. She calls it an "experience-mapping project," as people can submit stories - or read others or learn about the park's history. When you submit your story, you drag a marker to the part of the park you want, describe what happened, when it happened, and can even add a photo. This will probably be the wave of the future - just add Podcasts and videos, and this will become a time capsule.
We wrote about Alexis's awesome AdScape project last December. And he two main sources for the historical information are Around Washington Square by Luther S. Harris and It Happened on Washington Square by Emily Kies Folpe.