a dog park and access to the lake for canoeing and fishing. The Ann and Roy Butler Hike and Bike Trail forms a complete circuit around the lake. A local nonprofit, The Trail Foundation, is the Trail's private steward and has built amenities and infrastructure including trailheads, lakefront gathering areas, restrooms, exercise equipment, as well as doing Trailwide ecological restoration work on an ongoing basis. The Butler Trail loop was completed in 2014 with the public-private partnership 1-mile Boardwalk project. Along the shores of Lady Bird Lake is the 350 acre (142 ha) Zilker Park, which contains large open lawns, sports fields, cross country courses, historical markers, concession stands, and picnic areas. Zilker Park is also home to numerous attractions, including the Zilker Botanical Garden, the Umlauf Sculpture Garden, Zilker Hillside Theater, the Austin Nature & Science Center, and the Zilker Zephyr, a gauge miniature railway carries passengers on a tour around the park. Auditorium Shores, an urban park along the lake, is home to the Palmer Auditorium, the Long Center for the Performing Arts, and an off-leash dog park on the water. Both Zilker Park and Auditorium Shores have a direct view of the Downtown skyline. Barton Creek Greenbelt The Barton Creek Greenbelt is a public green belt managed by the City of Austin's Park and Recreation Department. The Greenbelt, which begins at Zilker Park and stretches South/Southwest to the Woods of Westlake subdivision, is characterized by large limestone cliffs, dense foliage, and shallow bodies of water. Popular activities include rock climbing, mountain biking, and hiking. Some well known naturally forming swimming holes along Austin's greenbelt include Twin Falls, Sculpture Falls, Gus Fruh Pool, and Campbell's Hole. During years of heavy rainfall, the water level of the creek rises high enough to allow swimming, cliff diving, kayaking, paddle boarding, and tubing. Swimming holes Austin is home to more than 50 public pools and swimming holes. These include Deep Eddy Pool, Texas' oldest man-made swimming pool, and Barton Springs Pool, the nation's largest natural swimming pool in an urban area. Barton Springs Pool is spring-fed while Deep Eddy is well-fed. Both range in temperature from about during the winter to about during the summer. Hippie Hollow Park, a county park situated along Lake Travis, is the only officially sanctioned clothing-optional public park in Texas. Hamilton Pool Preserve is a natural pool that was created when the dome of an underground