An example: for your photo, some perfect key-subjects would be monastery, or religion, or church, or cat.
Sorry I didn’t understood that is an obligatory part, @davidesimoncini. I thought it was only necessary to fit into two given themes. On the other hand, you have listed all four possible key subjects. So, I would go with two general: Religion and Cats :)
Have I qualified now? Should I edit the comment with my photo?