While in the area looking for Arago,look for this one too.
The Ruins are leftovers of a a WWII observation post which was used to see if any Japanese forces were coming ashore !
The ruins are three rooms about 12 x 16 feet with two taller towers (and maybe more I didn't see !).
I discovered this place when coming down the trail but you may want to see it going up the hill....it makes for a good rest stop.
This is one of the few areas along the trail with a view of an open sky. If I remember correctly, it is above the viewpoint where there is a bench.
I found out later (from a docent in the nearby estate gardens) about the history of this spot.
The gardens are a nice virtual cache too !