The castle is supposed to have been erected by Sir Ralph Lumley, who obtained licences from Richard II. and Bishop Skirlaw to embattle his house of Lumley. It is in arrangement a square courtyard, surrounded by a quadrangle. Two of the fronts, the south and north, measure 65 yards 1 foot in length, the other two 58 yards and 1 foot. Oblong towers, of greater height than the main portions of each front, from which they project, strengthen and guard each corner. The most exterior angle of each tower is capped by a buttress.
The west front is the oldest existing portion of the castle, and is supposed to have been the Lumley manor-house, before Sir Ralph extended and added to it.
Originally the east side of it, that looking into the courtyard, was the principal front, and in its centre the gateway, flanked by semi-octagonal turrets, may still be seen. The front of the gateway is formed of two arches, the outer segmental headed, and the inner one pointed. Between these is the groove wherein the portcullis ran. The arch leads to a vaulted passage which entered the original courtyard. On the north side of the passage is a pointed doorway, leading into a narrow corridor, having a latrine at its east end, and connected originally with the gatekeeper’s room.
The present gateway is in the centre of the east front, and has incorporated with it an earlier round-headed archway, with semi-octagonal jambs and moulded imposts. On either side of it is a square turret, surmounted by octagonal machicolated parapets, the alternate sides of which are embrasured.
The turrets are joined by a machicolated gallery, defended by a battlemented parapet. Above the door are six sculptured coats of arms. Between the two highest, Neville and Percy, is the royal coat of Richard II. Below is the Lumley coat, having on the sinister side the arms of Grey, and on the dexter the coat of Hilton. The shields are all surmounted by the respective family crests.
A room on the south side of the gateway contains in its centre a flag, which on being raised leaves open the entrance to a vaulted chamber about 10 feet square and some 16 feet deep. From the existence of a latrine, and a little ventilation from a small unglazed loophole looking into the courtyard, it seems to have been intended as a safe place for the custody of prisoners.
In the north-east tower are two rooms, divided by a modern partition, and showing evidence that they originally formed the private chapel of the family. The south-east tower contains on its second floor the state bedroom, in which King James I. is said to have slept when he visited Lumley.
In the north-west tower is the famous kitchen, which Howitt described as "one of the most stupendous, lofty, and every way remarkable kitchens in the kingdom." The south-west tower contains the banqueting-hall, celebrated for its very fine stuccoed ceiling, part of the work initiated by Richard, second Earl of Scarborough.
Between the towers on the west side the main building forms the baron’s, or great, hall, which probably remained unaltered from the time of Sir Ralph to the early days of the century before last. The fireplace is the work of John, Lord Lumley, and is decorated with the family arms, impaling FitzAlan. Here also is a large equestrian statue, representing Liulph, a traditional ancestor of the house. There are also a series of interesting family portraits.
Not far from Lumley, Lambton Castle stands on the northern and opposite bank of the river. The original home of the Lambton family was, however, on the same bank as Lumley. According to an old view, it was a double house of stone, with flanking, gabled wings, and the grounds laid out in parterres and terraces. It remained the residence of the family, until it was dismantled in 1797 by William Henry Lambton, who had adopted Harraton Hall as the family seat.[12]