RPG Insanity

Okay… This game is an EXE Create game which means I need to grind A LOT. Back in Asdivine Dios, I managed to grind a lot thanks to you guys.
Is there a place where you can grind levels while playing through the normal ending and being a Freemium?

Thanks in advance

Some dungeons has hidden rooms where you can fight powerful monsters, as well islands around the overworld. It's been ages since I played this game so my memory is fuzzy.