Sainte-Chapelle
The narrow spiral staircase by the entrance takes you to the upper chapel where the famed beauty of Sainte-Chapelle comes alive: 6,458 square feet of stained glass are delicately supported by painted stonework that seems to disappear in the colorful light streaming through the windows. Deep reds and blues dominate the background, noticeably different from later, lighter medieval styles such as those of Notre-Dame's rose windows.
The chapel is essentially an enormous magic lantern illuminating 1,130 biblical figures. Besides the dazzling glass, observe the detailed carvings on the columns and the statues of the apostles. The lower chapel is gloomy and plain, but take note of the low, vaulted ceiling decorated with fleurs-de-lis and cleverly arranged Ls for "Louis." Audio guides (€3) are available, or you can download a phone app focusing on the church's stained glass windows.
Sunset is the optimal time to see the rose window; however, to avoid waiting in killer lines, plan your visit for a weekday morning, the earlier the better. Come on a sunny day to appreciate the full effect of the light filtering through all that glorious stained glass. You can buy a joint ticket with the Conciergerie: lines are shorter if you purchase it there or online. The chapel makes a divine setting for classical concerts; check the schedule at www.classictic.com.