OlliOlli World

All you need to do is select Gnarvana on the map on the far right hand side and select the black podium icon "The Gnarvana Portal". Next, go through the conversation, join a group, play the level and set a score. The league rotates once every 24hrs. So, once you have set your score, come back the next day, and upon entering the league menu again, and the achievement will unlock. If it does not, it is likely due to you not setting high enough score. However, with that said, my first time doing this I came almost last but I still unlocked it.