Runes are found in the Tower Of Trials. The Tower consists of Tiers. 1 key is needed for every Tier. The tier consists of 7 stages, every next stage is more difficult than the previous one. Additional keys will be added to a players account every 20 hours with a limit of 2 pieces.
The tower currently consists of 80 levels and there are 20 tiers. You have 3 attempts to defeat the level in order to progress to the to the next stage of the level.
1 - Shows the floor you are currently exploring and at what stage of the floor you are on.
2 - Shows the recommended power level for the stage and the difficulty.
3 - Shows how many attempts you have left for this stage.