So I’m at the beginning of chapter 2 in Tales of Xillia. I found this neat levelling spot outside of the main story available just before the end of chapter 1. When the game asks you to go to Felgana Mines, you can instead head north into Old Vicalle Mines. There’s no mention of this location anywhere so far except for a man in Leronde telling you to avoid it. Naturally, I ignore the man’s warning and proceed to explore the optional area.
Old Vicalle Mines has some extremely high level monsters for your current level (which I’m assuming to be approximately 25 – 30 if you haven’t been avoiding enemy encounters), but it also has some very valueble materials and items. I managed to survive encounters there once I reached level 30. The trick is to always circle strafe or sneak up on enemies so you approach them from behind to trigger a battle where the enemies start stunned and at half HP. Then just spam all your most powerful artes (hopefully to hit elemental weaknesses). You’ll be getting tons of EXP and high-point material drops. For added effect, use EXP boosting food.
If you’re only around level 30, avoid the Gentlemen and that Devil Beast, Roparde, roaming the central chamber. Make sure your equipment (especially weapons) are significantly high (at least weapon shop rank 30).
Once you reach level 35 or so, you can start taking on Gentlemen who give even more EXP! I’m currently at level 40 after only two hours of grinding in Old Vicalle Mines. But avoid Roparde even if you do reach level 40 though, he’s an optional boss meant for level 60 and above.