3D printed icicles with LEDs inside can make a beautiful DIY Christmas decoration. It's cheap and easy to do.
I've bought the cheapest LED strip online and used individual icicles. I've modeled a special channel inside the nut that prevents water from coming in. Then you simply screw in the bottom part and hang them outside, but they work great indoors as well.
For easier printing, the screw comes with a smaller hook or ring that you print separately. This was done so that you need almost zero supports. If it was combined, you'd need to use a lot of supports.
I've made a video about the design process and how everything was put together. Check it out here (7min):
I've printed the bottom (nut) part of the icicle normally and the actual icicle was done in vase mode. This is easy to do with some slicers, like Simplify3D.