Ah, La Grande Arche ! Have not been inside - it houses some Government offices, and I believe F. Mitterand had it built so that its inauguration would coincide with the bicentinary of the French Revolution - thus 1989.
I don't think one can go up to the top anymore - need to google just to be sure.
Has anyone ever taken a trip (by boat) in the Sewage of Paris (les Egouts de Paris) - Well worth it ! I went there when I was about 10 and I am not sure it still takes place - Another info for Google.