A pen or pencil holder in the hyperboloidian fashion. Not that there is a lack of such here, but... well...
Anyway, after inserting the pens, my daughter immediately put it on top of her head and decided it was a crown, hence the name.
Note that such a move is a bad idea unless the fit is tight, because the pens will slide down.
If you happen to have 30 pens with no more than 9 mm diameter, you can use the attached stl file.
Otherwise use the customizer to adjust various parameters. (Updated!)
It is possible to skip infill completely. With two perimeters and three top layers I got a sturdy result with perfect top surface. However, the inner circumference delaminated a little because of shrinkage.