Book of a Thousand Days, by Shannon Hale
This is one of my favorite books by Shannon Hale, right after Princess Academy. It's a retelling of an old fairy tale (Maid Maleen). The basic premise is a princess refuses to marry the prince her father picks out for her because she loves another, so he locks her in a tower for seven years. This particular retelling is from the POV of the maid, not the princess herself, which makes for an interesting take on everything. I really liked the culture sketched by Hale - it's loosely based on Mongolia, but it still feels like its own unique culture.
Some of my book group commented that the princess in this retelling is very unsympathetic. This is undeniably true, but the question remains whether that is a good thing or off-putting for readers... in the end, for me I think it works to the advantage of the characters' development, and I found it easy to tolerate it until that character development becomes apparent. This is in part because if I were in the maid's shoes, I probably would not be very sympathetic to the princess myself. However, My sister in law felt that it made the POV character unsympathetic because she had no sympathy for the princess, which made it hard for her to connect with either one. I think each reader is going to have a slightly different tolerance level of that sort of thing. By and large though most people I have talked to about this book have enjoyed it, so if you like fairy tale retellings, you should give Book of a Thousand Days a try. Plus it has a cat in it.