It looks unimpressive from the outside but once you step inside you realize how huge it is and that you are actually finding yourself in a monument that is a 1000 years old. It's pink bricks and white stones alternate in disorderly fashion, many edges of blocks are chipped, may have been for centuries, it's slightly damp and dark inside (Romanesque style churches had heavy walls which supported the entire structure and therefore could not allow large windows as Gothic churches did). You feel like you're in a cellar or some dump but you're actually in one of the hotspots of the pilgrimage to Compostelle! The crypt is well-conserved and is totally extraordinary (though you have to pay a couple euros to visit it).