McKinney Falls State Park
A park for nature-lovers on the east side of Austin, south of the river. Facilities include a dining hall with a kitchen and 12-odd picnic tables; camping grounds and barracks for the troops. Beyond those amenities it's Texas wilderness with all the trimmings, making it a great place for a wilderness quest-type event. Apocalypse Austin currently uses McKinney Falls as the "in character" site for their games (usually played at a UT game site). AA has also learned a valuable lesson--don't play "blob tag" late at night in a park full of tree stumps and cacti.
In 2000 McKinney Falls charges an entrance fee and a $6 parking fee for overnight parking or a day visit, and puts fees on use of the bunks at roughly $15 a head and dining hall rental at $75 (this is from memory--Apocalypse Austin was able to host 100 people here for about $30 a head for two nights, three days, not counting food.)
From Texas Parks and Wildlife McKinney Site: Directions: The park is located 13 miles southeast of the State Capitol in Austin off US Highway 183. Take McKinney Falls Parkway south, off US Highway 183, straight to the park entrance. Camping fees vary; entrance fee. For reservations, call 512/389-8900.