When getting near level 20 you will need ashen crystals, a nice and easy place to farm them are at "Yosun Temple" - which is located in Northeast Asia (more specific at the Ruins of the yellow River, east of Beijing).
The ashen crystals and other items drop from the "Headless Warriors" and "Headless Soldiers", the punisher ones doesn't drop ashen crystals (according to the monster info), but you can still engage them - as there will often be a warrior and/or soldier in that group - giving a small chance for a drop of ashen crystal.
The headless ones range from level 13 to 15, which makes them fairly easy to farm!
Example of five minutes grinding while writing this:
-
10 x ashen crystals
-
4 x enchant box
-
2 x Commodity Box
-
4 x Spirit Equipment Box
Farming for a longer time will give more though, and the exp ain't bad for leveling up lower level characters, such as when you get the monk/viking.
Summarise:
Location:
Northeast Asia, Ruins of the yellow river (east of Beijing) - Yoshun Temple (first room you get in when entering the temple).
Creatures to kill:
[Melee creatures] Headless Warriors and Headless Soldiers, the Headless Punishers doesn't drop ashen crystals.
Drops:
Ashen Crystals
Spirit Equipment
Commodity Box
Enchant Box
Giseng (good for leveling potions)
Healing and mana potions
Notes:
These creatures doesn't group up, so you can safely attack a single group and expect only to meet 4-6 creatures that you have to take out.
They don't use spells, only some runes (which you can break easily).
They are headless

So you should be able to take out them due to lack of brain from their side
