A rainbow stacker is one of the most open-ended toys there is. A few ideas to start:

  1. Stack it as a rainbow, then upside down as a boat.
  2. Line the arches up as a tunnel for cars.
  3. Make beds for small animals.
  4. Build a bridge between two blocks.
  5. Sort the arches by size.
  6. Rock an arch like a cradle.
  7. Trace around the arches on paper.
  8. Make a fence for a farm.
  9. Roll a ball through the arches.
  10. Stand them up as a city skyline.