At the battle zone go to the resort area. if you go to the one building with the swimming pool next to it and you go in, the lady will stop you and tell you to leave. if you really want to go and see whats inside then use the explorers kit and go underground. just walk around and go back up at a certain spot. Youll know where to go up at because there will be writing on the wall that says "go up". So go up and you will be inside of the building. but dont let the lady see you because she will make you leave and you will have to do the whole process over again.