The dark and mysterious forest
on the eastern edge of the Shire
, in Middle-earth
It was formerly part of a great forest that stretched all across the continent. It is now (that is in the Third Age when Lord of the Rings takes place) much reduced, but still houses strange things. Old Man Willow, also called the Willow-man and Old Grey Willow, is a powerful malevolent tree in the centre of it, in the valley of the River Withywindle, which induces sleepiness and confusion. The Withywindle joins the River Brandywine, the border of the Shire.
Tom Bombadil, the magical and unique character who is a power for good and is unaffected by the One Ring, lives in the Old Forest too, with Goldberry the river's daughter, and they probably know where all the best magic mushrooms are to be had, by the sound of them. Toujours gai, Frodo, toujours gai!
Just beyond the Old Forest are the Barrow Downs, the tombs and burial mounds of ancient kings, where the Barrow-wights now lurk.