These are 4x4 post caps I made for our gate and fence outside. They're about as simple as you can get. I spray painted mine with that textured hammered metal stuff. It would be fun to add a gargoyle on top of them or something. Snug fit on wet posts and slides on easy for dry ones. Use a bit of construction adhesive to make sure they stay on over time.
Took about 3.5 hours to print at a fast setting.