Reccomended 3D engines for learning?

I’ve downloaded a couple of OpenGL-based 3D engines from the site, and am having a hard time figuring them out. Very comprehensive code, but with minimal comments and almost no documentation on how the classes work, what method XYZ is used for, etc.

I don’t suppose those engines were geared toward instruction and tutorial use. Fair enough, but could someone reccomend some 3D engines which help guide the reader through some of the details involved? Thanks for the advice.


First try or