Go to Valley of Fire in winter. It's stunning, but too hot even this early in May. It was 91 degrees and the signs bluntly warned us not to hike or risk death.
The wildlife refuge has a really clever display where one side of the actual stream running through it is plexiglass, so you can watch the little fish.
The two previous nights the temps went below what had been predicted, so we got a motel each night. Had planned to camp this last night, but we just weren't up to the heat. So that's why I'm in Vegas waiting now for close to two hours just to get a light in my hotel room.