Twyfelfontein
This national monument and UNESCO World Heritage site is home to around 2,000 rock engravings, estimated to be close to 6,000 years old; it's extremely rare for this many paintings and engravings to be found at the same site. The entrance fee includes a knowledgeable guide who narrates the timeline of the landscape and the people who lived here. Start early (it's hard to make out some of the art in full sunshine), bring binoculars, wear sturdy shoes, and bring lots of water (at least a liter) and a hat.