This might interest many here; Humble Bundle have a collection of digital copies of a series of books relating to the National Parks in the USA. https://www.humblebundle.com/books/national-park-service-100th-anniversary-book-bundle Humble is a simple site that has a tiered purchasing option; hte first level is whatever you want; then the next two levels (that give you more books) have specific thresholds that you have to pay over to unlock the content. It's an honest site and one I've used a fair bit; their forte is in computer games; but they've also branched out into books on varied subjects as well as comics and now this bundle.
