I got into building RC airboats when I got bored... I'm an engine nut, and acquired a few airplane engines free of charge. With some time, some wood (or foam or plastic or whatever strikes your fancy), an engine, and a few props, you can build an airboat that will scoot across the local soccer field as fast as a monster truck. If you have a pond close by, even better yet.

I've built 4 so far, with a 5th one in the works. I run engines from .29ci to .90ci and have a blast. My .46 powered modified flat bottom runs about 5mph slower than a ProBoat Impulse 31 BL. Pretty good considering my airboat is a pound heavier or so..

I am also getting into airplanes. I have 8 or 9 running aircraft engines so it was a no brainer to try flying them one of these days. I have two planes, and one is an ex-Army target drone.