In this task we got a large text file where obviously was a substitution cipher.
Text analysis tell us that it is readable text but no one script or Cryptool couldn't solve it correctly. This task was one of cheapest so we decided to find another way.
NCN is Spanish CTF game so text most likely on Spanish. Ciphertext is quite large so it can be story or novel. What Spanish novels are wide known? Google showed this to us. Of course "Don Quixote" is well-known novel!
We found this novel on Spanish. After comparing given text and novel we finally convinced that our hypothesis is right.
_I PI LP-C) R_ LC NCIQFCA R_ QPG! I!N:)_ I! ,PU_)! CQ!)RC)N_A I! FC NPQF! ... En un lugar de la Mancha, de cuyo nombre no quiero acordarme, no ha mucho ...
So we had restored substitution of cipher and found flag in text by searching substring "NCN".