Located on the top of the Montmartre hill, looking like a big and round cake (oriental inspiration), it is visible from a few places in Paris and outside. It's also a beautiful spot for a view over Paris.
The building of the cathedral was ordered to remember the 58 000 victims of the Germano-French war of 1870-1871 (under Napoleon III) and the "Bloody Week" of the Commune in Paris. The work started in 1875 and finished in 1914.
To reach the church, you can climb the stairs or take the "funiculaire", which is a sort of lift or téléférique. You can also climb up the dome to have an even higher view of Paris. You need to buy a ticket at the vending machine outside of the basilica. The entrance of the dome is on one side of the church. Free entry for the basilica. 5 euros (adult and children) for the dome.