Based on the popularity of the 10 Penny Puzzle, I did some research to find a more challenging penny packing model.

This is it... your goal is to put 16 pennies (mint pennies provided with puzzle) into the quadrant sized opening.   There is one unique solution and the pennies will just fit. They use 74.7% of the available area. Good luck finding it quickly… I think 20 minutes would be an excellent solution time.

Base is cut from floorboard for durability, water and scratch resistance and to give it a nice weight and feel.  Top section is birch ply. 

Solution is provided with the puzzle.