I have something different and challenging to offer that I hope you'll all find interesting/amusing. Warning: if you find it difficult to remember kata already, please do not attempt this as it will ruin your coordination.
The challenge is to perform the kata inverted. That is, practise the kata how it would appear if you were to watch it in a mirror.
Taking Pinan/Heian Yondan as an example: instead of turning left as the first move, you would turn right. Instead of stepping forward with the right, you would do it with the left.
Try it with Nihanchi first to get the concept, then move onto others once you get confident. You'll end up with your body screaming at your mind, your mind yelling at your body. There may be moments where you know you're doing something right because it's wrong, or wrong because it's right. :D
Nothing practical here, just a bit of fun and mentally taxing. (Although it can be a great prank to invert the kata when practising with someone to seriously confuse them).
I'd like to know how you find this/which kata you struggle to invert. Personally I find Chinto a nightmare to do this with.