The basilica of the Sacred Heart of Paris, commonly known as Sacré-Cœur Basilica is located on the highest point of Paris, on Montmarte. The basilica is built in neo-romano style, and it is definitely worth seeing, though you need to walk up 234 stairs to get to the top of the 130 meter high Montmarte. But, the view is totally worth the stairs.
They started the construction of the church in 1893 and it was finished in 1919. It is now one of the most visited churches belonging the the Catholic Church in France.
It is free to enter the church, and the church can be visited every day between 6 in the morning at 10 in the evening.
Sacre Coeur Basilica pictures