The Twilight Grove sits in the middle of Duskwood. It has a surprisingly night elven feel to it, and could very well be sitting dead in the middle of Ashenvale as opposed to in the middle of human lands. It is home to one of the four portals to the Emerald Dream guarded by the green dragons of Ysera's Green Dragonflight.
The world bosses known as the Dragons of Nightmare can be found here. Interestingly, this is the only of the four spawn points not to have any other dragonkin patrolling around. However, this might be due to it being in Duskwood and low level players can quickly discover a large dragon seen from the entrance.
The Twilight Grove also contains a Moonwell.