Castle Hill, more formally known as the Hope Gallery, was originally supposed to be a hotel. The company installed concrete slabs for foundation, before learning the hill was too steep to support a high-rise. The contractor abandoned it and it became a canvas for local graffiti artists.
During the day you can admire the artwork of local graffiti artists. At night you can climb to the top and enjoy a alternate nice view of the Austin Skyline, while chatting with friends or meeting locals.