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.
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.