Grosmont is one of the Three Castles, three neighbouring forts in Monmouthshire, south Wales, mostly built by Hubert de Burgh in the early 13th century, in what was then part of England. The castle was briefly involved in defence against Welsh insurgencies, but for most of its working life was used for residential purposes, until becoming derelict during the 16th century. Like the other two castles (White, Skenfrith), the place has a peaceful, rural setting - beside the little village of Grosmont, on a low ridge between the main road and the River Monnow.
Although Grosmont Castle was never very large it has a pleasing variety of architectural features, in different states of decay, including two towers, a tall chimney, a two story hall block, a gatehouse, and walls in a range of heights, and is entered via a wooden bridge across the encircling ditch, once the moat. All is lined by trees and grassy slopes, and the site is not often visited, in part due to the rather remote location, away from major roads.
Grosmont is 12 miles northwest of Monmouth and 3 miles from the busy A465 between Hereford and Abergavenny, but is reached by a much quieter road, the B4347. The castle is near the middle of the village, on the outside of a wide bend along the River Monnow, and is accessed via a short lane opposite the local post office. There is no designated parking, though spaces are usually available along the main road. The castle is open all year except over Christmas, and no entrance fee is charged. About one hour is sufficient to see the ruins.
The first defensive structure at Grosmont was a basic, wooden, motte and bailey castle, constructed soon after the Norman conquest, and little changed for over a hundred years, apart from addition of the hall block. Ownership was transferred from the crown (King John) to Hubert de Burgh, the 1st Earl of Kent, as a reward for service; he rebuilt the remaining timber sections in stone, initially between 1201 and 1205, but mostly, following a hiatus during which time he was for a while imprisoned in France, after 1219 - at this time the towers (originally three of them) were added, together with the curtain walls and the gatehouse. Like many other buildings from this period hereabouts, the castle was constructed out of the local Old Red Sandstone, typically coloured grey with reddish tints. In 1239 the castle reverted to the crown and was a few decades later passed to the Dukes of Lancaster, descendants of Henry III. Modifications were carried out to make the place more suitable as a residence, including addition of the north range on the site of the north tower, and expansion of the southwest tower, making it five stories tall.
Despite occupying a fairly prominent position, overlooking the river, at ground level Grosmont Castle appears somewhat enclosed, partly because one section of the adjacent ridge is slightly above the base of the structure, and because of the surrounding woodland, which was not here in medieval times. A short walk down the lane and across a field reaches the entrance footbridge, which leads to the remains of the gatehouse, on the southeast side of the castle. The gatehouse now consists now only of low walls, though was much more complete as recently as the late 19th century. Like the majority of the structure, the gatehouse dates from between 1220 and 1232, during the second phase of ownership by Hubert de Burgh. To the west is the main part of the castle, including the southwest and west towers, their connecting walls, and the northern range. The southwest tower is largely complete, though still missing part of the walls and all the floors. A short series of steps takes visitors through the grand entrance door of the tower and up to first floor level, connecting with a 40 foot-long walkway on top the westernmost castle wall. The upper walls of the southwest tower contain several windows, fireplaces and chimneys, reflecting its later use as a residential centre. The remains of the northern block, on the far side of the castle, are dominated by a tall, slender chimney, topped by an elegant, octagonal tower - once connected to a room that is believed to have been the private chamber of Eleanor of Provence, wife of Henry III. On the east side of the castle is the hall block, the oldest visible part of the complex, probably built in the late 12th century. Its walls retain their original two story height, and the building has a variety of interesting features including doorways, windows, the base of the lower floor dividing wall, and part of a spiral staircase to the upper level. The main hall once occupied most of the top floor, next to the smaller solar room, which was used as sleeping quarters.