Direct Comparisons:
* The answer was as clear as day.
* The answer was as simple as a child's toy.
* The answer was as elusive as a ghost.
Figurative Comparisons:
* The answer was like a key unlocking a mystery.
* The answer was like a beacon in the darkness.
* The answer was like a breath of fresh air.
The best simile for "answer" will depend on the specific context and the type of answer being discussed.