Sanctuaries are Dark Fox clan camp. This is the place they live in and get prepared for raids in. No one but the Dark Fox clan may enter this place, if he/she does, he will get a 3 day ban and loose all items + the persons chest will be unlocked. You can recognize it by a sign that must be placed in front of the sanctuary saying "Dark Fox Sanctuary, leave or be banned". Tunnelers are the ones that take care of the sanctuary the most.