Wraithmarsh is a swampland present in Fable II.
The area known as Wraithmarsh is a long winding path from the Cullis Gate Sparrow arrives in to Bloodstone. Along the way, the player encounters creatures such as Hollow Men, a Banshee and Balverines. On the first trip, a Troll can also be encountered.
Oakvale now is just part of the sea, which rose and consumed the town. The entrance is blocked off, meaning that Sparrow can't swim in the area Oakvale once was at.
A pre-Wraithmarsh Oakvale is seen in See the Future. It is fully explorable, although The Hero of Oakvale's house seems to be demolished as the path from the bridge doesn't curve to where the house was supposed to be.