Braunschweig, Germany ( an excellent collection of textbooks, which is strongest in the fields of history, civics, and science. While the library’s holdings are particularly rich in terms of German textbooks from the 19th and 20th centuries, there are also materials from throughout Europe. Additionally, the GEI offers short-term research grants to visiting scholars to use the library (and a pleasant guest house for those working at the Institute); web site:
http://www.gei.de/en/georg-eckert-institute-for-international-textbook-research