first of all you should go hiking, duh (bring water)
When in Joshua Tree, there’s nothing better than exploring the great outdoors and communing with mother nature, and the very best place to do just that is Joshua Tree National Park. There are two entrances to the park on this side: one is in 29 Palms, and the other is in Joshua Tree. Pick an entrance, and drive the route that connects to the other entrance. Stop along the way anywhere that catches your eye to boulder or hike – you can’t go wrong. If you have time, divert from your route a bit and visit the Cholla Cactus Garden, you’ll see acres and acres of teddy bear cacti and meet the friendliest little ground squirrels! If you have more time, escape the crowds and go for a longer hike, some favorites include 49 Palms Oasis, Lost Horse Mine, and Keys View.