Journey into the Interior of the Earth
Wikisource, like it’s sister Wikipedia, is a free library of public domain information.
Including, ‘but not limited to’, this 1877 translation of “Journey to the Center of the Earth” by Frederick Amadeus Malleson.
“This 1877 translation by Frederick Amadeus Malleson is considered the most faithful, though it has some slight rewrites.”
Yes, you can read the entire Jules Verne book right there online. Nifty.
I haven’t explored it thoroughly, but I imagine there’s a lot of cool, open information there. Public domain is awesome.