Outlaws of Sherwood Forest is book 47 in the Choose Your Own Adventure series. It was a book written by Ellen Kushner.
You are spending the summer at camp. One night you steal into the woods to find a lost arrow. Suddenly a cloud covers the moon- and you are magically transported to Sherwood Forest. You're standing face to face with a marksman dressed all in green. It's Robin Hood, and he needs your help! The sheriff of Nottingham has captured Maid Marian!