I am interested in using some 3D images for a lesson I'm developing for kids, in which I want to show them various printouts of 2D cross-sections of the image and have them try to figure out what the higher-dimensional form is. What 3D image I use is not particularly important, just needs to have an appropriate level of complexity (and some other properties I won't bother describing). I would like to avoid the hassle of creating something from scratch.
Is there an online source of fun 3D images people have created that I would be able to use for this, that are in the public domain?
A secondary question: what is a straightforward way to output cross-sections of a given 3D image in a printable format?