Golden Key

I love the worldbuilding in this book. The occasional bits of created language are just close enough to Spanish that anyone should be able to recognize what the characters are saying in the context of the conversation, rather than needing it spelled out by the authors (and happily, they don't seem to find it necessary to provide blatant translations, except occasionally). The mythos behind the painters is rich and well thought-out, and it is interesting to see how it is intertwined with the politics of the region.

The book can be a bit daunting when first picked up, as the prologue is a detailed description of several paintings that don't mean anything to the reader initially, but they are all explained in the course of the book.