One simply can't go to Paris without a visit to the Eiffel Tower. The engineering alone is remarkable. Though there is a fee for the ride up, it is well worth the money. While taking the elevator to the top you get a fabulous close up look at the structure internally through the glass windows. Once on the upper level, the walk around roof allows for 360 degree views. From the Arc de Triomphe to the north, to the Sacre Coeur Cathedral on the hill to the northeast, to the towers of Notre Dame due east, to name just a few, the panoramic vistas are nothing short of magnificent.
I strongly recommend to buy your ticket online, and reserve a time of visit. That way you can skip the horrendous queues.
Photos taken with Sony DSC-HX50B.