Leaf Tower
Complete the game, save the clear data then head on out back to the map. Select the Ruins of the Dragon Race dungeon, and watch the cutscene. On its completion, hover the cursor over the area north of the Fortress City Palladium dungeon, back on the world map, and a big ol' tower should appear.
Unlock Mercenary Classes
Hunter - Requires level 10 archer.
Minstrel - Requires level 20 hunter.
Druid - Requires level 20 magician and level 15 priestes.
Musician - Requires level 20 paladin and level 20 archer.
Paladin - Requires level 10 magician and level 10 fencer.
Seer - Requires level 15 magician and level 20 priestess.