Track trapdoors: a handcrafted marble set with a whole back of trapdoor track. Build it with 233 building pieces and 10 marbles.many gear gadgets: consists of a wheel lifter,a stair stepper, 4 straight rails, trapdoors and a block track. Intricate system of cogs, gears and wheels, full of crazy twists and turns.stem concepts: learn principles of science,technology, engineering and mathematics(stem)hobby & gift: precise laser cutting ensure you a fluent building experience. Also a great gift for family and friends.