The kids are back in school, leaving Central Texas' many outdoor attractions to the grown-ups. But temperatures remain high enough that enjoying the outdoors can turn into a sweat fest — unless it's planned right.

Take advantage of smaller crowds and almost-outdoor-but-not experiences at these Central Texas spots, all less than a two-hour drive from San Antonio.

Austin Nature and Science Center
This sprawling facility in Austin's Zilker Park caters to kids, but that doesn't mean it's not fun for everyone. Adults also can enjoy its hands-on educational exhibits and recreational activities designed to increase awareness and appreciation of the natural environment. Sure, there are live animals, a pond, and a dinosaur dig outside, but there's plenty to do inside as well. The Naturalist Workshop displays tables of fur, rock, bones, plants, and insects that visitors are encouraged to touch (you know you want to). And make sure to check out the temporary Nano Exhibit, an interactive experience where visitors can interact with things unseeable to the naked eye.

Longhorn Caverns State Park
Walking tours of the caverns last about 90 minutes and cover a variety of rooms and formations. Best of all, the underground temperature remains 68 degrees — no matter the season. Tours cover geology of the cave system and its rather checkered history, including tales of prehistoric visitors and legends of treasures hidden by outlaws. In the 1920s, one of the rooms even functioned as a dance hall.

McKinney Roughs Nature Park
Best known for hiking, biking, ziplining and other outdoor pursuits on its 1,000-plus acres, this park also has a visitor center indoor exhibit hall featuring local wildlife, including a tiger salamander, three-toed box turtle, kingsnake, and a baby alligator. Catfish, largemouth bass, spotted gar, and Rio Grande cichlid swim in a 1,000-gallon aquarium. Terrariums housing the land animals are built into an artificial-rock wall and, another area features a large manmade tree, bringing the outdoors inside. A built-in touch table has fossils and artifacts visitors can handle, something not always possible (or wise) to do outside.

Science Mill
Housed in an 1880s feed mill in Johnson City, this facility uses technology-based exhibits, games, and programs to help people learn about and appreciate science. The Paludarium in the lobby is a contained ecosystem of living elements such as mosses, plants, crabs, and fish, and non-living elements of water, air, and rock. And an Aquaponics Greenhouse combines aquaculture or raising fish and hydroponics, or growing plants in water without soil.

Meadows Center for Water and the Environment
Part of Texas State University in San Marcos, the Meadows Center includes Spring Lake, a collection of springs that fill a dammed lake and form the headwaters of the San Marcos River. Glass-bottom boat tours are a cool way to see the springs at the bottom of the lake, as well as the plants, fish, and other creatures living in the freakishly clear water. Inside Discovery Hall, chill out with a 1,000-gallon aquarium of native fish, along with an endangered species exhibit featuring Texas Blind Salamanders, San Marcos Salamanders, and Fountain darters, plus a baby turtle aquarium and an interactive exhibit about the Edwards Aquifer.