As a little boy and now as a big boy I love ramps.  My son and I were sitting in the living room last night playing with marbles.  An urge came over me to make the play more dynamic and the thin sheet of styrene plastic I had stashed in the garage popped into my head.  I ran and found it then placed it against the couch and the floor creating a smooth arching ramp.  We played and played with that ramp rolling the marbles up and down, side to side, launching them into the air.  It was just as I remembered from childhood.  A very simple game that teaches complex physics.  Momentum, gravity, acceleration/deceleration, strength and coordination. To name a few.  Plus the sounds.  As the marble runs up or down the plastic ramp the pitch changes with the speed the marble travels.  A fantastically absorbing play opportunity!