They do not charge. Yes, you can go inside. But the REAL interiors treat is a little shrine outside and to the left as you face the main building. A little chapel just filled with candels and statues. It's very cool. When I was there last I made the huge mistake of shooting it on Velvia, and the contrast just killed the picture. So prepare for high contrast. It is always breezy in the chapel and the candles flicher a lot, so you might also plan for a long exposure to turn the flickers into more of a glow. I think you'll be happy.