If I couldn't feel any pain and was indestructible for 24 hours I would launch myself into space. I would float around the galaxy. I would sit on the sun or swim into a black hole. I would just observe space because I would love to see something that I would otherwise never get to see first hand. I would be the only person ever to be able to see space close up without something separating me from it. No glass, no spaceship, no telescopes and no suits. Just me and space.
If I had to stay on earth I would go to every place that seemed impossible to physically explore and see with my own eyes. I would go swim at the bottom of the ocean or with sharks, then it would explore inside a live volcano or walk through fire just o see what it would be like. Or I would j jump off the empire states building so I could see what it would be like to fly. I would do anything an everything I couldn't normally do an I would experience all of the things I couldn't normally experience.