[Turtle91]

“ePub” is simply a standard used to distribute electronic books. It specifically packages all the book contents, images, styling, fonts, etc. plus a couple administrative documents into a .zip like folder with a .ePub file extension. You can easily confirm this by renaming and changing the file extension from .ePub to .zip. Then you can easily browse all the internal documents.

The contents of the book are indeed html… or, more accurately, xhtml - which is a stricter version of html.

It would be counterproductive to load individual html files into your reader. You would be missing all the other files necessary for a good reading experience. If your device can use the ePub format, then just use that.

Having said that, files on Gutenberg, especially older ones, can have atrocious coding in the html used. I, like many others here on MR, spend time cleaning up that html coding so it displays much better. Free ePub editors like Sigil or “Calibre Editor” allow easy access to the internal files while keeping the administrative files, and the overall ePub, standards compliant.