Here's a challenge: memorize all the prime numbers up to 10,000.
One possible way to do it:
Take every prime number image and then set it on fire. 7043 for me is an axe chopping up a suit of armor. I could just set that compound image on fire. Then when asked if a number is prime, I could just check whether it had been set on fire. Repetition would cement the image modifiers...
I like Simon L's analogy that he used for his memory system, that could also apply to this memory challange:
Let's say you have 10 coins in each of ten boxes. On each of these 100 coins, there is a different date. Let's say in the first box you pick a coin with the date 1978 on it. Now, instead of memorizing the number, you just toy with the coin until it gets slightly heated up with your body heat. Now, you do this with one coin in each of the ten boxes. Once finished you can go back to your first box and touch all your coins. The one that is slightly warmer than the others is the coin you have memorized.
If anyone attempts this, please leave a comment below! :)
I've marked the level of this challenge as "intermediate", because it requires a working mnemonic system for numbers.