How about adding some new terrain types, such as:
Fjord – riverbeds with shallow water tiles light blue in color(traversable but with penalties), and deep water tiles darker blue in color(non-traversable) interspersed with rocky tiles.
Sandy Beach/Coastline – sand with movement penalties interspersed with some grassland.
And although not native to the European theater in which the game is modeled…
Desert – dunes
A wise general wins before the battle, while the ignorant general must fight to win - Zhuge Liang