Dear Nemo,
I don't know about the correctness of "a woods" but I very much like its poetical sound. Around here we use "woods" to mean a stand of trees less large (that would be smaller wouldn't it) in acreage than a forest. There is an area of about an acre covered with large trees, maples, one big oak and some trash trees just down the road from where I live. Children play there all the time and tell their parents they are going to play "down the woods."
No help at all, was that?
wow