Still scratching your head over this year's GCHQ Christmas challenge?
This year the public has been challenged to decode the names of UK landmarks, testing skills including codebreaking, maths and lateral thinking.
The annual brainteaser aims to tickle the neurons of those hoping to work in intelligence, and comes in the form of a Christmas card, sent by the national spy agency's director Anne Keast-Butler.
To help you solve it, we've spoken to a few puzzling experts to pick their brains on how to navigate the testing challenges.
Have a read and don't worry - we haven't given away the answers.
