There are 2 mazes: one for ser and one for estar. From the start, choose the words/phrases they would associate with the given verb. Follow the route until there are no valid options. I chose not to tell them where the end is, but you could always mark it if you wanted. The answer keys are provided.
Additionally, I often use this as an in class activity. Instead of having them write on the paper, they use small slips of colored paper to cover the boxes. I save the copies to reuse in future classes and it's very easy to check.