The Sandstorm will be available once you have reached level 500 and the light world dungeon #28 was cleared. It is located in the dungeons and contains 100 monsters which have to be fought with your main character.

This dungeon has a special feature: the next floor can be fought for free if an enemy has been defeated and you still have at least 90% of your hit points left.

Enemies defeated in the Sandstorm will be added to your scrapbook if you have not defeated them previously.