The Internet Archive is one of those places online that can suck you in for hours. Old films, concert recordings, old radio shows, lost websites and, of course, books.
Now I'm not one for reading ebooks (though electronic versions of reference books are a different story). However, I am one for downloading vast swathes of bizarre old publications from the Prelinger Library ("a private research library open to the public ... Its collections encompass some 50,000 books, periodical volumes and printed ephemera.") and boggling at the contents. Here are a selected few books, their covers and sample innards, to give you an idea of the sort of fascinating, peculiar and occasionally bonkers things they have there. Some have great covers or endpapers. Others are just nuts. Occasionally they fall into both camps.
First a few books found through pursuing one of my obsessions. In every case, click for a nice, big, readable version.
And here are the rest. I tried dividing them into broad categories, but it was beyond me.
UPDATE: Like a fool, I repeatedly called it the 'Preminger' Archive in the original post, under the influence of watching old Otto Preminger movies. Thanks to reader Ctorres for the correction, and for Rick Prelinger for pointing out it is, in fact, the Prelinger Library that houses printed works. Sometimes this brain just doesn't work.