At certain times (ask at the information office) some volunteers from the church accompany you to the attic, where few frescoes are still visible after the remodeling of the church has hidden. It's an interesting and exciting visit that let you see the building from the top. The nearby cloister is just as beautiful.
The Church is a must-see but everything around it as well, such as the tower in front, the cloisters next door, and especially the FRESCOES. Only problem is that they seem to be open only for the summer season nowadays. The Priory is also remarkable for its use of brick. Anyway, it's free and picturesque.