Engines hide all the fun stuff. It's nice when you just want to get a game made, but if you want to get into 3d you can start by making your own soft 3d engine,

Engines hide all the fun stuff. It's nice when you just want to get a game made, but if you want to get into 3d you can start by making your own soft 3d engine, eg. no 3d api, only cpu. Hand code the 3d to 2d (screen) transformation. Write your own code that decide what color the triangles should be in. Then when you understand the domain, you can look into the low level 3d hardware api layer eg. WebGL for the web.