Natural hot springs – man made structure. Each room contains a warmer area of the spring. The final room is definitely spa/Jacuzzi temperature. 15-20 minute bus ride from the corner of Casa de la Luz and Hidalgo (or about a $10 cab ride). There are about 3 different sets of springs on the outskirts of town - each catering to a slightly different crowd. There is one spring that has water slides and other installations for kids - but I think we will probably have to make a trip there as well. The coldest spring is probably around 80 degrees Fahrenheit.