A international airport would make it easy to bring in supplies and troops without drawing unwanted attention and you can have a escape plane on stand by for a quick escape for when the authorities decide to stop by. Go to Comment
The PCs see a large oak tree, a curious species of yellow and black butterflies swarm around it. Upon further inspection they find that the tree is hollow and that there is an underground cave in it from which the butterflies appear. Will they inspect this strange cave?