Lufia: The Ruins of Lore is a single player experience.
It should be easy to find Lufia: The Ruins of Lore for the Game Boy Advance available for purchase. Lufia: The Ruins of Lore was released in 2003.
After you can enter the Ancient Cave, buy yourself a suit of Bronze Armor and the best weapon that you can buy at the moment, kill off your party members and get have the main character train as a Swordsman. Get him to level 10 and enter the Ancient Cave, if you can defeat the boss on floor 9, you'll get 6000 experience, make sure you have a providence because the monster on floor 12 will be able to do 80+ damage to you. I was level 25 and it was doing 97 damage to me. Repeat this process to gain levels very quickly. It's also a good way to master classes, I've mastered 4 already.
20100 EXP In Ancient Cave...
In the Ancient Cave on the 17th floor is a floor boss called the Parasitic Cell, if you've learned Miracle Hit and are above level 23, you should be able to defeat it by using Miracle Hit every turn. It has 1250 HP so you'll be fighting for a while. If you win, you will receive 20100 EXP.