Serving as the source of the San Marcos River, Aquarena Springs discharges 150–300 million gallons of water daily and is the focal point of Texas State University’s Aquarena Center (921 Aquarena Springs Dr., 512/245-7570, www.aquarena.txstate.edu, 10 a.m.–5 p.m. daily, $7 adults, $6 seniors, $5 children 4–15).

For much of the 1900s, the area was a resort and entertainment park known as Aquarena Springs, featuring amusement park–style rides, water shows with mermaids, and Ralph, a pig that swam around in the river performing amazing tricks. Texas State University purchased the aging theme park in 1994 and transformed it into a non-profit nature center dedicated to conserving natural resources and educating the public about the role water plays daily life.

The park has a natural aquarium with local endangered species and archeology exhibits with 12,000-year-old artifacts. One of the most popular attractions is the glass-bottomed-boat tour, offering a spectacular view of the bubbling San Marcos River springhead and the plants and animals that rely on its cool, clear water.