if you found number 12 well done - that was well hidden.
Now head towards the green shack in the far left hand corner of the field where there is a snicket down the side of the cottages.
The cache is down here in something hard
Update: seems people were having trouble extracting this so I have put a little loop on the lid to grab it with - it's just wrapped round the cover so don't drop it !
Please put back in place when you replace the cache and cover it up with some vegetation. Thanks