Click to ENLARGE and read here. Wikipedia: en.wikipedia.org/wiki/Monhegan_Island_Light
Google Map. Click to ENLARGE. My preferred right. See text below.
Located on the highest point on Monhegan Island, the Monhegan Island Light, is impossible to miss. It is an iconic and compelling landmark just to the east of the dock/village and completely dominating the view above the village.
From my experience and I visited it at least 5 times, thrice in one day, it is not hard to get to — much easier than it looks.
Thanks to a tip from a local I found that cutting across the cemetery was the quickest way to get there — and you get the added bonus of being able to explore the historic and serene cemetery with some classic headstones. See map above. There is a latched gate that you have to open (and close behind you). The path to the top, not used much is overgrown BUT is definitely NOT difficult to traverse in either direction.
The view is rewarding. I did see one sunset from there. That was worthwhile. Despite my many trips I never made it to the museum — one of the reasons being that it closes around 3:30pm.