The Towering Wood is a large region of forest that is located in the Eldeen Reaches, and is sometimes used synonymously to refer to the Reaches. Legends say that the Towering Wood is as old as the world, and was (and remains) home to the First Trees. It is home to enormous trees, larger than can be found anywhere else on Eberron, from which it derives its name.
The Towering Wood is surrounded by a buffer zone, several miles wide, where the trees are smaller and the vegetation less thick, and this region is generally considered to be safe. The farmers and other folk in the eastern reaches will use these buffer zones, but they generally don't cross the line into the deep wood itself. The Towering Wood is ancient, infused with primal power and dotted with manifest zones. You can feel it the moment you enter it, and it is home to all manner of dangers.
There are several species of tree that are unique to the Towering Wood, such as the awe-inspiring Bluewoods and the Greatpines (of which the Great Druid Oalian is one). Sparsely located throughout are the Titans, absolutely enormous trees (some thousands of feet tall) that are beacons and wellsprings of primal magic, each one unique, and a wonder in its own right. It is possible that these are indeed the first trees, and each of them are the center of the Lamannia manifest zone.
The Towering Wood is home to a large variety of flora and fauna, as well as aberrations, fey, fiends, and undead. Many of these threats are tied to manifest zones, but others were introduced to the Wood centuries ago and have carved out their own niches.
The Towering Wood is home to many small communities, some of which are associated with the various druidic sects of the Reaches. These communities don't practice industrial agriculture, but they do cultivate and maintain the land around their homes to ensure they have enough resources to survive. Typically, they are highly competent, they know the Wood better than anybody, and they know what is and isn't safe to eat, as well as where (and what) it is safe to hunt.