In DBZ Online, there is special solo dungeon to gather materials for making equipment. These dungeons are called Trial Dungeon.
Trial Dungeon can be accessed at Lv 30 and comes with 2 difficulties: Normal and Hard. And just like Fight of Dragon Ball, Hard difficulties are available once you cleared Normal difficulties.
Unlike other dungeon in DBZ Online, you can keep your progress in Trial Dungeon if you failed in clearing the Map. As long you don't reset the Trial Map, it will stay just the way you enter it last time.