Sainte-Chapelle is a Gothic chapel on the Île de la Cité whose upper level is almost entirely made of stained glass. More beautiful inside than Notre-Dame — and infinitely more missable if you hit it at the wrong hour.
Sainte-Chapelle is one of those rare places that earns every superlative thrown at it — but only under the right conditions. The stained glass is genuinely exquisite, widely considered more beautiful than the interior of Notre-Dame Cathedral. The catch: it's a notorious choke point, and a mid-morning crowd can turn a transcendent experience into a shuffling queue through a dim antechamber.
Yes — it has one of the most beautiful interiors in Paris, arguably more stunning than Notre-Dame. Just don't arrive mid-morning without a plan; the crowds undermine everything the stained glass is supposed to do.
It's ticketed — exact prices move, so check before you go. It is free on the first Sunday of each month, but expect heavier crowds on those days.
Arrive at least 30 minutes before opening to beat the queue, or use a Paris Museum Pass to skip the ticket line. Treating it as your first stop of the day is the single most effective thing you can do.