Bowser's Castle MKDS custom map mod
Whilst going through some mod folders I found this gem. One of my first custom map attempts from a few years ago. Featuring some animated models for some parts of the track. Feel free to decompile and use for any projects. As it was a first attempt the collision was done in not the right way, hence why roads don't really work with it.. oops. But it still plays good. Will work for just driving around + multiplayer fun.
Note: There also isn't any triggers to get back on the track. You'll have to reset using the mission select.