Well done, you've solved cipher challenge number two. This type of cipher is a special substitution cipher known as Atbash, and is made by reversing the alphabet and replacing the last letter with the first, the penultimate letter with the second, and so on. It is called Atbash because it was originally done with the Hebrew alphabet, and it took its name from the first and last, and second and penultimate letters in that alphabet.
Substitution ciphers replace the letters of the message with other letters. Caesar shift and Atbash are fairly simple substitution ciphers to crack, because once you've made a few guesses it's easy to spot the system that has been used to decide on the substitutions. The next message won't be quite so easy to crack, so remember to look for punctuation, single letters and short words.
Finally, the keyword to access the third challenge is teacake.