Forgotten Wolrd is new dungeon that came with Legend VI.
You need atleast lvl 35 to enter there, and a portal stone that can be pbtained from monsters called "Envy".
There also is different kinds of FW dungeons.
- Lvls 35-70 Togui Village (Earth Ghost Town)
- Lvls 71-90 Flame Mountain
- Lvls 91-110 Shipwreck
In forgotten world you can find talismans, witha quest, and all talismans from certain dungeon; you can get SoX weapon, different for each levels.
I dont know if theres a time limit for entering to Forgotten World again.