It's located on the Ile de la Cité, inside the old Royal Palace courtyard (today the Palais de Justice).
In 1241, King Saint Louis (Louis IX), ordered the building of this chapelle to house Jesus Crown of Thorns and a fragment of the True Cross. He payed more than three times the price of the building to get this treasure from the Constantinople Emperor! The reliquary holding the fragments of the True Cross was destroyed during the Revolution, but today, the Crown of Thorns is in the Treasure of Notre-Dame.
The stained glass windows, restaured in the XIXth century, are from the XIIIth century and cover a surface of 620 m2! It shows scenes of the Old and New Testament. It's beautiful when the sky is clear, and when the sun goes down, but it's the most crowded time. You can also bring binoculars to admire the details of the highest stained glass windows. To avoid queuing too long for the tickets, it's better to buy a twin ticket at the Conciergerie and start by this monument, which used to be a Royal Palace and a sadly famous prison.
Opening time: March until end of October, 9.30 a.m until 6.00 p.m (last entry at 5.30 p.m). The rest of the year: 9.00 a.m until 5.00 p.m.
Prices: free under 18 years old; 6,10 euros for adults. Ticket including the Conciergerie: 9 euros.