Watch Tower
It is not really possible for you to inspect the details of the tower's construction from this distance, but there is no logical purpose for any of the current residents of the region to build such a tower here. The elves among you, and those of elvish heritage, know that in earlier years, this region was under elvish protection. What purpose there may have been at that time for such a structure is not known, but that certainly seems to be a possibility. The terrain around the tower is fairly open, with some low scrub brush and a few isolated taller trees. If the woods were very thick, it would not take much to obscure the tower.
Forward post? Sentry duty? Why is the tower here? These remain burning questions, but the answers are a mystery.
It will probably not be possible to approach the tower without being seen, if there are sentries manning the upper reaches, that is, but you see no signs of movement atop the tower nor through any of the few windows.