This is the southernmost of the tors that line the impressive Brent or Chapel Hill, high above the town of South Brent. It is one of the largest outcrops on the hill, composed of metamorphic rock, but the nature of the location within dense woodland means that only portions can be viewed at any one time, and it is quite difficult to gain a full perspective of its size.
Marked in an open access area on OS Maps, this doesn't seem to be the case as an impenetrable wire fence ascends the hillside from a rather broken gate below, where a bridleway enters the moorland from Lutton. The name of 'Underhill' might derive from the fact that the tor sits right down on the hillslope. The nearby farmhouse below is also given this name.
The Tithe Map for the Parish of South Brent simply notes Underhill Tor as 'Rocks' in plot 2164, and a closer look from the south-west side indicates it is bisected by a wall which is indeed the case. Clearly seen from directly above and from the neighbouring hills in the winter months, a wonderful view from the top can be obtained when ascending the tor from the north side, embracing the fringes of South Dartmoor including Ugborough Beacon and Eastern White Barrow. A small peculiarly narrow and elongated rock basin can be observed on the summit rock on what must be the most secluded of the rockpiles on this interesting hillside.