Haskell Free Library and Opera House straddles the USA – Canadian border between Stanstead, Quebec, and Derby Line, Vermont. This library was built in 1904 by the American Carlos Haskell and his wife, Canadian, Martha Stewart Haskell to over services to both communities. And while the library has a life marking the border along with floor, patrons are free to freely cross the border within its walls.
Librarians available to assist patrons can be either USA or Canadian citizens, or both, and most are bilingual.
Image info here.