It's no surprise that I love libraries. I'm an author, it's kind of what we do. But my love of the New York Public Library runs deep for a lot more reasons than just accessibility to books. The NYPL is an incredible resource for writers, especially those of us focusing on historical writing. The digital collection isn't entirely open (ie there are some resources you can only access while at a library location and with a valid library card), but enough of it that it's an incredible tool.
One of my favorite places to start rooting around for inspiration while I'm writing books is the digital collection's listings of fashion plates. If you're interested in the history of 19th-century fashion, this is the place for you. Godey's Lady's Book and La Mode Illustrée are both well-represented in the collection, and clicking through will give you a pretty good idea of how fashion (especially silhouettes) changed throughout the 1800s.