This Baobab tree in Western Australia has an opening on one side that leads into it hollowed out interior. It seems this tree and others like it have been used as prisons. This one has enough room to hold five prisoners.
Most of the he pictures in this blog are images that are listed in Flickr under the "Creative Commons" license for non-commercial use. All of the images are linked to their original Flickr pages where more information and comments can be found. There are also links to the photographers profile page on Flickr.