The aim is to build a model of a bridge using the blocks strewn below. The blocks need to be placed on the first one in the proper order as determined by the carved symbol on each block. Choosing a wrong block will make the whole bridge collapse.
The last block has the up and down arrows on it, and using these arrows the bridge can be folded down into stairs or back up. The lake should be drained using the cannon before the bridge can be lowered.