Sainte-Chapelle

King Louis IX, later canonised as Saint Louis, built the chapel between 1242 and 1248 to house the Crown of Thorns and other relics of Christ's Passion, which he had purchased at extraordinary cost from the impoverished Latin Emperor of Constantinople — reportedly a larger sum than it cost to build the chapel itself. Housing sacred relics of that stature required a building worthy of them, and Louis wanted it finished fast.

That speed was made possible by an innovative structural system that pushed the building's load onto slender exterior buttresses and iron reinforcing rods, freeing the upper chapel's walls almost entirely for glass rather than stone. The result is fifteen soaring stained-glass windows, roughly two-thirds of them still filled with original 13th-century glass, tracing more than 1,100 biblical scenes from Genesis through to the Apocalypse.

The chapel was built on two levels with two very different audiences in mind: a modest lower chapel for palace staff and guards, and an upper chapel, reached by a narrow spiral staircase, reserved for the king and his court alone. Standing in the upper chapel on a sunny day, drenched in coloured light, it's easy to see why medieval visitors treated the climb as an ascent from the earthly to the divine.

The chapel didn't survive the centuries unscathed: during the Revolution its relics were dispersed and its spire torn down, and much of what visitors see today, including the current spire, is the result of a thorough 19th-century restoration rather than untouched medieval work.

Sainte-Chapelle sits inside the Palais de Justice complex on Île de la Cité, a short walk from Notre-Dame, which makes it easy to combine both into a single visit. Because it shares the complex with a working courthouse, expect airport-style security screening before entry, so budget a little extra time.

The stained glass is the whole point of a visit, and its effect depends almost entirely on natural light, so aim for a sunny day if your schedule allows — an overcast morning leaves the windows noticeably duller. Tickets can be booked online in advance to skip some of the queue.