I would love to see the surface of venus. If we could build something strong enough to last in that environment. The moons of jupiter and Saturn would be next. But out of the places that are actually possible, First would be the moon. I'd go back to the apollo 12 landing site and plant the flag again. And of course Mars. Though I'm pretty sure we are never going to find any living organisms on Mars, there is still the feeling of what if. No better way to look for it than actually walking on the surface and digging up soil.