:crazy: sorry to jump on your band wagon but where is the side undr the bonnet or in side?What engine is it? It's probably 'hiding' at the back of the engine. You have to unscrew the side, and then lift out or tip back the side of the filter box and then pull the filter out. If I can, I'll get some pic's for you tomorrow.
Welcome to the forums by the way. I've also moved your post to the heating and cooling forum where it will receive a wider audience.
When you say 'behind' do you still mean accessible and visible if you lie in the footwell?Does it have air-con. If so you'll find it in the passenger footwell, behind the glove-box. By memory I beleive there is one screw to remove and then you slid the cover off towards the centre of the car and then pull out the filter. Good luck