The Door to Where?

I was out walking in Pollok park yesterday with my friend Katy when we came across this curious little addition to an old towering tree just off the beaten path.
So today I grabbed my camera and took another stroll to investigate this wee door.
There is an outdoor nursery within the boundries of Pollok park who spend their days wandering about the woodlands and building lovely wee dens made out of broken sticks. I think this wee door is something associated with those little people. Perhaps a door to a fantastic new world? Finn certainly seemed keen on exploring!