Valhalla Ruins
Accessing Valhalla Ruins
Once you reach base level 60 you can enter Valhalla ruins. This is accessed via the Instance menu and offers 6 stages across 2 difficulties. Each stage and difficulty provides access to different MVP/MINI bosses depending on the chosen level range. Use this to select the bosses that drop the most valuable gear or items that you're looking for.
You can use the arrows to the sides of the MVP/MINI boss model on the right side of the screen to see each of the bosses that you'll encounter at that difficulty/stage.
Example of Elite stage 100 with Dark Lord as one of the bosses
Example of Elite stage 170 with Gem Spirit as one of the bosses
How Valhalla Ruins Works
This instance takes place on a map where MVP/MINI bosses spawn in the same 5 locations on the map shown below. These bosses are significantly easier than the world boss versions and give everyone in the party loot rather than just the MVP so this is a great way to target bosses for specific loot.
You can also spend lucky coins after any boss is killed to make a second roll on its loot table. Personally I would save those coins for ancient equipment but later on once you know what you're doing you may want to do this.
If you die you respawn at the entrance of the ruins and can try again. You can leave at anytime and try again later in the week too so if you can't do all five bosses in one go.