On my final day, I headed north to Saint-Denis. After checking out of my hotel, I opted to have my luggage stored for the day, since I don't have my flight until later that evening. I then took the metro to head all the way to the royal basilica.
This is a Gothic church, which was completed in 1144. Before that, the site was a Franco-Roman cemetery, and sure enough, if you go underneath the crypt, you can still see these archaeological remains. But nowadays, this church is significant because plenty of French kings, as in every king from the 10th to the 18th centuries, are buried here.
The church can be visited independent of the burial places. The area with the buried kings are actually separate and has a specific entrance ticket for it, but I say it's definitely worth it. There's plenty of things to see. After all, the royal tombstones are rather lavish and opulent, as the above photos indicate. When I die, I definitely don't have such flair, but for these kings, it is a must.