I designed this bridge puzzle for the Maker Faire Vienna in April. It is inspired by the sketches of Leonardo da Vinci and holds together without any glue, nails or screws thanks to interlocking pieces in the easy version and only due to friction between the parts in the hard version.
For both versions I uploaded a file containing 7 sets of pieces (bridge_xxxx_7x.dxf) which is enough for building a reasonable sized bridge. If you want a bigger one you can cut more pieces using the files for one set (bridge_xxxx_1x.dxf).
You can read a bit more about it on my blog: https://regendrogenbogen.wordpress.com/2016/06/25/da-vinci-bridge/
If you don't have any access to a laser cutter at all, you can buy the kit on Etsy: https://www.etsy.com/shop/DaVinciModelShop