Help Decrypt this Clue

[walther]

Ok so I'm working on a game/Treasure Hunt. I believe I can blame Jazz for this one, since I'm pretty sure he pointed it out a long time ago. If you're interested in joining the hunt check out
http://www.greathunt.com/
Buy the book and support the cause....

This is the message as posted on their facebook page
13,24,16,20,7,17,19,2,9,17,23,17,15,25,6,25,14,23,20,9,22,6,13,8,15,3,8,13,13,22,4,6,15,1,7,8,2,24,14,10

What is really annoying me is that it should be a simple encryption. Based on the others it's not an overly complex cipher. Though I'm guessing it's 2 to 3 different types stacked:
Manipulate the numbers (add a sequence or key)
Convert to Letters
Then possibly a Caesar Shift or reverse text

I can't for the life of me get this. I don't know if I'm making it too complex or what. This is their hint for solving it (also encrypted, but very easy to solve)
Eulctsalehtnierusaelpruoydnifot
Odtsumrehpicnoitiddaelpmisa
Gnissimsawtahwybdnuofeblliwerusaerteht
Gnicsinimerdnaerehtsitahwgnieeston

Help!!!! Before I lose my mind. I'm sure, I'm going to be kicking myself once I get the method

One thing, if you solve it please don't post the solution here, just PM.

Just consider it your birthday present to me

[ReVoRabbit]

have you tried unfiction? there is a whole group dedicated to decryption and cyphers.

[allardwza]

...there was a thread devoted to this a couple of years ago over here... FWIW - no mention of your code though...

allard

[Paradox]

42?

[RichAE91]

42?

nice

[walther]

hahah 42? If only

Well technically this isn't a clue from the book itself. It's just a hint they posted on their facebook page. So, the unfiction thread that died out 2 years ago probably won't help but good thought!

Just threw this out here, as a diversion from the Gold

[Ginger]

add one, convert, see "what's missing"? (didn't try it)

it says addition cipher... not sure how to add (to) them (together), or what's missing

[walther]

Took me little longer than it should have, but I finally cracked it
Now that I know the solution, it's obvious that if you are not involved with the hunt you're not going to be able to solve it. The key is in the book. Sadly the clue was something I already knew so it didn't help me at all.