Pontifex is can only barely be called a game. There are levels, sure, but that’s about all this thing has in common with a ‘game’.
So what is it? It’s a program for building bridges. You are presented with a river and a budget and have to construct a bridge that will not only span the gap, but also allow a train to be sent across it. Get the train across and you go to the next level.
It looks extremely tedious and boring, I know, but it’s really not. Getting to play with the physics engine and watching the car and the bridge fail in catastrophic new ways not only teaches a bit about bridge architecture (I know! Making a game fun and educational? Devious!) but is endlessly fascinating to watch.
Don’t believe me? Check out the demo here