The hidden places were both created by the fae and by the magic they used to create the new worlds. Almost every world has at least one hidden place, some of which were created in order to allow the fae to experiment more and others by the magic so that those viewed as dangerous or were in trouble could find somewhere safe. Unfortunately, or fortunately for some, these places can only by those with the ability to walk through doors, whether that ability is natural or not, although there are a few that are totally cut off from the web almost all the time.