Armadillo Run – a fun, realistic physics-based puzzle game (2006)

Armadillo Run is a physics-based puzzle game in which you build structures to lead the armadillo to the exit of each level.

Gameplay: https://www.youtube.com/watch?v=uH4SS2oG_uc

I spent hundreds of hours playing this game. The physics were so fun to exploit, you could literally complete a level in a hundred different ways. I realised it hadn't been submitted on HN before, which is surprising considering how good it was.