I went for a walk with my son and daughter yesterday, down along the banks of the River Wye. There is a wonderful old Willow tree that must have been hit by lightning or something. Two sides have split apart, leaving the centre of the tree with a burned out hollow that you could climb through if you were small enough.
My daughter Dorothy, a great fan of Narnia and all things alter Univers-ey and Lord of the Rings, was dared to climb through, and so she did.
She has been though the heart of a willow and reports that nothing has changed in the universe on the other side except maybe coffee tastes different with the new kettle!