This site contains the volumes of the Bansenshukai, a classic ninjutsu text, in PDF form. To view them, you will need a PDF viewer for your platform. If you don't already have a viewer, you can find links below. Many thanks to Rob Boger and John Lindsey for making these available.
For those who don't know, the Bansenshukai (which translates to something like "Ten Thousand Rivers Flow Into the Sea") is a multi-volume set of "secret" ninjutsu knowledge written by Fujibayashi Tasutake of Iga in 1676. It contains information on everything from philosophy to weapons to tactics to astrology.
The copy that you find here was scanned from photocopies made of the copy in the national archives in Japan. They have been assembled into PDF for ease of viewing. Please note that these are large files, and can take a long time to download. If you prefer not to deal with the long download, copies are available on CD for a nominal fee (contact me for details).
Note: These are the original volumes, in the original Japanese. You can, however, buy a nice printed English translation done by Anthony Cummins on Amazon, available for Kindle and in hardcover. You can find it here. Note that I have no association with Anthony or Amazon, but I do own a copy and recommend it. I do not know of a complete free English translation, and Anthony's book is reasonably priced, especially considering the effort it must have taken.
Due to US export restrictions, you may need to download a separate encryption module for your viewer. The encryption modules for Xpdf can be found here and the modules for ghostscript can be found here.