Montmartre's sugary white church with a view.
To be honest, the real reason to come to Montmartre is to wander round its narrow streets and absorb its villagey atmosphere but although the crowds can be nightmarish it's also worth taking a look at Sacré Coeur because the sugary white church sitting at the top of the hill is one of those buildings you suddenly glimpse in the distance from some of the most unlikely spots in Paris, because the interior is a glorious bit of kitsch and because it is part of Parisian history. It was built between 1875 and 1919 as an act of penance for France's defeat in the 1870 Franco-Prussian War and paid for by public subscription. The Romano-Byzantine style basilica has a clutter of domes, equestrian statues of Joan of Arc and St Louis over the portico and a vast glittery mosaic in the apse. If you've got the energy, you can climb up to the top of the dome, although the views are also pretty good from the parvis outside the church.