Witnessing the [almost] impossible

Spinning off from the Reiffel Tower, what other spectacular things would tourists want to see? I think it could fall into two main categories; extreme & rare natural phenomenon and extreme, rare and new science.

Natural Phenomenon

Since the dawn of man people have put special value on seeing rare and extreme events of nature - from the mythical powers of the eclipse to the spectacle of lightning. Today we have a more commodified version of it - travel companies tailor holidays around the notion of 'extreme tourism' - whether its visiting an active volcano, ice diving or flying over the Chernobyl zone. Maybe we have to unite 'conventional' and 'extreme' tourism with a series of proposals and parasitic structures.

Extreme Science

This category is a hybrid between the demonstrations from the Royal Institution Christmas Lectures and the witnessing of nuclear testing. In an age were we can't distinguish between reality and special effects, we should try to design experiences to cause awe and amazement in the audiences. It should also capture the feeling you had when you played with your chemistry set... i guess its trying to capture Arthur C Clark's Third Law of Predication - Any sufficiently advanced technology is indistinguishable from magic.