My answer would be The Moon
Why?: Well, The Moon has at least a little bit of oxygen so people should be able to breathe as long as they are in their suits. The problem is, mars doesn't have water, and it doesn't rotate. So ageing would either be faster or slower on The moon. At least you can get a good view on the moon.
The Moon should take something around 3 days to get there. Since the moon doesn't rotate, one side of the moon is hot and the other side is cold, while one side is dark and the other side is lighter. The moon is a odd place to go on but if it were for one day, The Moon is a good answer
