If you live in Austin and have not visited the Congress Street Bridge, affectionately known as the bat bridge, you need to go. If you are visiting and the bats haven't left for the winter, this is a must-see for you too. One of the most unique and celebrated attractions in Austin is a naturally occurring phenomenon and costs absolutely nothing to enjoy. The 1.5 million Mexican Free-tailed bats that live under the Congress Street Bridge from March to October emerge at dusk in a breathtaking display. Austin's bats migrate every spring from Mexico, and have made their home under the Congress Street Bridge by the thousands since 1980.