There’s a fascinating collection called "The Fantastic in Art and Fiction" over at the Cornell University Library’s website, featuring nearly three hundred woodcuts, engravings, and paintings on fantastic themes such as "Demons", "Fantastic Space", "The Grotesque", and more.  This image is a woodblock of "the demon who gives knowledge of languages", from the book Dictionnaire Infernal, published in 1863 in Paris.

I was also interested to see that the collection includes a number of images on the themes of "Weird Science" and "Fantastic Space".  This cover of an old issue of Amazing Stories features an illustration from Jules Verne’s A Journey to the Center of the Earth:

It’s got a sea monster, and sea monsters are always cool.  This cover depicts the explorers being attacked by one of the creatures that inhabit the Inner Sea in Verne’s novel.

It’s a great collection.  Lots of fodder for your imagination. Check it out.