In November 2012, I had the good fortune to participate in a conference at the Royal Society in London. A colleague told me that guests of the Society could visit the library where rare books and manuscripts were held and that I could see the original folio of Newton's Principia Mathematica.
After filling out a form to become a temporary member of the library, then another form to request books, then another form to request this book, waiting 10 min for a librarian to bring it out on a cart and sign one more time, I was given the original handwritten manuscript of Newton's Principia Mathematica. It was transcribed by someone else (in Latin, to my chagrin) but annotated and corrected in Newton's own hand; note the corrections of the text in the pictures. I also examined a first edition of the printed book, of which photos are shown here. Annotations to this volume were made by a contemporary of Newton's. It may seem a sin to show a photo with my own hand touching the pages, but you had to turn the pages somehow! They gave you wipes to clean your hands before opening the folio and the book.