1. Bourges Cathedral
The sheer width of this structure hits you before you even step inside. Unlike the vertical rush of Chartres or Paris, Saint-Étienne spreads out, using a unique design with no transept that lets you see down the entire length of the nave uninterrupted. The double aisles create a forest of pillars that feels endless, and the 13th-century stained glass is so dense it actually darkens the interior even on sunny days. It is the anchor for all other Bourges attractions, visible from almost anywhere in the marshes below.
You need to look closely at the portals before entering. The "Last Judgment" tympanum is terrifyingly detailed, showing devils dragging souls into a boiling cauldron, a stark contrast to the smiling angels on the other side. Once inside, pay attention to the astronomical clock, which has been ticking since 1424, and the crypt, which is essentially a subterranean church in its own right.
Most visitors just do the ground floor, but the climb up the "Butter Tower" (Tour de Beurre) is non-negotiable if you want to understand the city's layout. From the top, you can see how the medieval center bleeds into the green wetlands of the Marais. It is 396 steps, and there is no elevator, so tackle this early in the morning before the heat sets in.