A simple cipher.
https://www.gchq.gov.uk/files/GCHQ%20Christmas%20Challenge%202024.pdf
We are given two words as part of the clue:
PERHAPS READING the start of this substitution cipher will help you solve it.
ISKGWIM KSWEBDU BN DFN LBIGSKSE BM IKBCWKBQX W QSWEBDU BDEBLWNBFD NF XFO MFQPBDU NGBM WECBNNSEQX ESPBFOM BDBNBWQQX ODKSWEWAQS CSMMWUS.
Once deciphered, take the first letter of each word:
PERHAPS READING IT NOT CIPHERED IS PRIMARILY A LEADING INDICATION TO YOU SOLVING THIS ADMITTEDLY DEVIOUS INITIALLY UNREADABLE MESSAGE
Answer: PRINCIPALITY STADIUM