Perched on the hilltop of Montmartre, the Basilica of the Sacred Heart is one of the most emblematic monuments of Paris. It's nicknamed "grosse meringue" (big meringue) due to the travertine stone it is built from, which constantly exudes calcite, which ensures that the basilica remains white even with weathering and pollution. Ultra-resistant, this stone has the particularity of being non-spongy, meaning that water cannot seep through. In contact with rainwater, the rock secretes a white substance that hardens in the sun. In the hundred years of its existence, the façade of this monument has never been renovated!