Gene Wolfe's The Shadow of the Torturer is the first book of The Book of the New Sun.
I enjoyed this book very much and I can highly recommend it to everybody, who wants to read a book, which has been written for adults. This book is a masterpiece and it's one of the best fantasy and science fiction books ever.
If you haven't read The Shadow of the Torturer, you should read it. I'm sure that you'll enjoy it.