Tower of Valni/Lagdou Ruins
These are extra places you can goto in between chapters, they are pretty good for leveling up units and getting more money.
::Tower of Valni::
This becomes available pretty early in the game after you select which Lords story you will follow.
Not all floors are available at first, you must beat certain chapters to progress higher up the tower.
Floor 1: Beat chapter 8
Floor 2: Beat chapter 9
Floor 3: Beat chapter 10
Floor 4: Beat chapter 11
Floor 5: Beat chapter 12
Floor 6: Beat chapter 13
Floor 7: Beat chapter 15
Floor 8: Beat chapter 15

Floors: 8
::Lagdou Ruins::
The Lagdou ruins are unlocked once you beat the story, select continue mode in the extras section on the main screen.
The enemies are very powerful in the ruins but is an excellent place to train units, escpecially promoted units.
Floors: 10