So what could be better than a toy that combines marbles with building?
Swiss company cuboro has created sets of beech wood blocks that do just that. Nicely natural wooden blocks fit together in all kinds of configurations to create sliding, turning, and twisting runs for marbles.
The standard set comes with 54 blocks. There are solid cubes, cubes with straight runs, cubes with top channels, and some with various twisting and turning tunnels. There are also various extension kits with other cubes and accessories.
Word of caution: There are marbles involved, so don't get this for children under 3 who still put everything in their mouths.
Available at The Wooden Wagon and other online stores in the U.S.