There are two guards by the library trying to keep lookie-loos from wandering in and seeing the treasure, but you come up with a good distracting story about what a strange phrase "lookie-loo" is. While they're pondering it, you sneak past them. You immediately realize the treasure isn't IN the library; it IS the library. This is the priceless Amber Room of first the Prussian rulers, and then the Russian Tsars. It ended up here in this castle, somehow. Incredible. You can see why they were trying to keep people out, but what are you going to do now that you're in?