what abount room of spirit and time? I suggestion this: create an event that you can entry at a dungeon with random mob with this rules:
-all empty texture (so good if will be all white screen).
-In this dungeon there are only mob lvl X (x=lvl char) without drop item and zeni
- only into the dungeon there is 300% exp bonus.
- You can enter in this dungeon only for 1 hour and 1 once per week
- you can enter alone without party (this is training like db)
You guys are you ok with this? If anyone have other suggestion, let a feedback