20 pieces, 60 edges, 8 tab/slot keys, 1 solution.
The pieces are engraved with text (not shown) describing the various levels of hell in Dante's Inferno. These can be used as a hint for the solution or just some twisted humor while trying to solve it. Start with "Abandon all hope, ye who enter here" and continue to the last ring.
Brackets on the inside hold the puzzle's shape.