Nichibunken Databases isn't a link that sounds promising, but oh, what a treasure trove of old Japanese art it is. Among the many lovely collections is the Japanese folktales in foreign languages, another has maps, which is probably easiest to browse by decade, then there's the picture scrolls (some nsfw), and also illustrations from an 1870s world tour. That's just a small taste of what's there. If, like me, you don't read Japanese, often you'll be going in with scant information of what will be on offer, but even random stumblings will reveal beauty and wonder. Just to get you started, here are nearly 800 pictures of demons and over 2500 floating world woodprints. [Note: Blue dots mean the material is accessible to the public, red dots mean you have to have a login to see it]
The Essence of Line is a collection of over 900 drawings by French artists "from Ingres to Degas" by the Baltimore Museum of Art. I'd link to some highlights but the site did such a stellar job of it that I'll just direct you there. They also have some sketchbooks. Note that some of the drawings have short essays about them. As a related link, here is the famous Demonographia, with drawings of demons by Louis Breton and descriptions by Collin de Plancy.