Here I'll show you how.
Open char_battle.cpp and search for:
Code:
if (to->GetMapIndex() >= 660000 && to->GetMapIndex() < 670000)
Code:
if (to->GetMapIndex() == MAPINDEX) iExp == 0;
Code:
if (to->GetMapIndex() == MAPINDEX) iExp += iExp * 10 / 100;
in this case it's +10% exp bonus but you can change the percentage by changing the number highlighted in red