I have at least a couple.

3D printing. But I mostly design my own models and mostly for utilitarian purposes rather than artistic. For instance, my mother’s into quilting and wanted a very specialized die for a Sizzix die cutter to use to cut quilt pieces, so I applied my amateur 3D printing, CAD, and mechanical engineering skills to the problem and designed/printed a die. The process also included making a custom tool for precisely bending the die blade.

Second, studying U.S. intellectual property law. I just dig it. And it’s relevant to me because I frequently publish software and models for 3D printing under permissive licenses. And I like having at least some amount of understanding of what the licenses really mean and what people will be able and not able to do legally with the works I’m publishing.