after beating the storyline get the friend area from wigglytuff caled southern isle's. And THEN go to Solar Cave, scattered across the floors in this dungeon are key's for secret doors. at floor 20 there is Surf in between some water get a fly or water pokemon to go across and get it. Now do a rescue job the next day a cut scene should appear (if not do another job) the scene will be about a robbery and some flying blue pokemon will zoom across you. after a little talk in town Northern Range will be unlocked. Its 25 floors of easyness. At the end there is Latios, also very easy to beat just throw things at him. After that another cutscene and then...
Latios will say he is sorry for theifing and he will tell you a little story about his little sis, Latias, and how she got her wing shattered from a peice of the commet you blew the crap out of. He will then unlcok Pitfall Valley , another 25 floors of easyness, but beware Pitfall Traps. No fight but you get Latias for free and her bro!