Perched atop Montmartre, the highest point in Paris, the Roman Catholic Sacré-Coeur Basilica (Gallery I) is a head-turning sight with its massive scale and unusual Romano-Byzantine architecture. It took almost forty years to complete, amid much debate and controversy, having been conceived as a symbol of spiritual renewal following France's defeat in the Franco-Prussian War and the uprising of the socialist Paris Commune in 1870-71. Its travertine stone continuously exudes calcite, thus keeping the structure white despite its exposure to weather and pollution. The landmark is perhaps at its most formidable when you're standing below it, debating whether to walk up hundreds of steps or spend 1 Euro to take the tram up the hill to reach it (I opt for the steps). Either way, it's worthwhile. As impressive as the church is from the outside, the interior contains one of the world's largest (and most beautiful) mosaics, "Christ in Majesty," and the view from the dome is, as you might imagine, spectacular. Afterwards, you can lose yourself in the winding backstreets of Montmartre, which still have some charm once you get beyond the obligatory tourist area.