This article at the Kildare Nationalist reports on recent claims by the Hill of Allen Action Group. They say that the hill is the site of two National Monuments (a cist and a barrow), which are within the land being quarried by Roadstone... continues...
The Hill of Allen stands out of the Bog of Allen like an island. It has an awful lot of folklore attached to it re the Irish mythical hero Fionn MacCumhail (who is often associated with the sun and brightness). There is room for about two cars to park on the south side of the hill coming from Kildare/Newbridge a little after a small power-plant on the left.
There are paths up the hill from here and the views from it are amazing looking over the bog of allen, into wicklow and the curragh and Cloghan Hill is interdivisable from here.
There is a lot of myth and legend attached to the Hill of Allen, it is called the birthplace of Fionn MacCumhail and it is said to have been the mythical Fiannas main fort. It is also associated with the god Nuada and he built a white walled palace on it.
It was called the Island of Allen because it is surrounded by the bog of allen.
It is also know as Almu. Almu is associated with a goddess/beautiful woman.
Fionn MacCumhail is meant to have throw Punchestown Standing Stone from here.
It is associated with Cloghan Hill and every year Fionn is meant to have sent a young warrior to Bri Ele where he was taken into the underworld to meet Brigdit.
I seem to remember reading somewhere as well that the tower folly built on top of it used a wedge tomb for its foundations but I havent been able to find I reference for this again.