This is cheaper than the better-known Eiffel Tower, and offers the distinct advantage of being the only place in Paris from which you cannot see the monstrosity of the tour itself. Of course, the writer Guy de Maupassant used to say exactly the same thing about dining half way up the Eiffel Tower. Next best great view: from the steps of the Sacre Coeur in Montmartre.
Nearest metro: Edgar Quinet; www.tourmontparnasse56.com/