The stairs have become a pretty popular place to play in our house. It began a few months ago with pretend naps on the bottom steps. Emily and Addison would lay down on a "step bed" and play "night night" or they would lay their babies down on the stairs to take naps.
Stair naps still happen, and a new game of laying a toy on each step has evolved. I'm not sure what exactly is happening during these games, but the placement of the toys is always very precise and seems quite purposeful.