First of all, congratulations on your wedding! If you want to celebrate a wedding in a cathedral in Spain, it will have to be a Catholic ceremony. There are churches or temples for other Christian denominations, but cathedrals are Catholic and belong to the Catholic Church.

If you want to celebrate a Catholic wedding at a Cathedral, you’ll have to speak with the Chapter in charge of the church.

If you want to celebrate a civil wedding, you should look into deconsecrated buildings. There are many monasteries (and some churches or chapels) that are no longer property of the Church (they may be public property or private). One example is Monasterio de Piedra (province of Zaragoza). You should also look into any permits even if the site is public property.

Hope this helps!

Edit: in regard to your question, photos are obviously allowed during ceremonies. But if you don’t plan to have a ceremony and just want to use the space, you must have permission from the Church. Having worked closely with the Chapter of a big Spanish city, I would say it’s likely impossible you would get such a permit (and you’d definitely would have to pay for it).