You wouldn't have missed Catedral de Valencia if you are visiting Valencia. It is just massive and…read morewith really interesting architectural details. You probably would have seen it's bell tower illuminated by spotlight when you wandering around town at night.
Interesting Fact from WIkipedia:
One of the supposed Holy Chalices in the world is revered in one of this cathedral's chapels; this chalice has been defended as the true Holy Grail; indeed, most Christian historians all over the world declare that all their evidence points to this Valencian chalice as the most likely candidate for being the authentic cup used at the Last Supper. It was the official papal chalice for many popes, and has been used by many others, most recently by Pope Benedict XVI, on July 9, 2006.This chalice dates from the 1st century, and was given to the cathedral by king Alfonso V of Aragon in 1436.
I was luckily enough to even have a glimpse of a late night mass going on.
A must visit if you are in town!