Brizlee Hill rises about 177 metres above sea level at the western edge of Hulne Park, the walled home park of Alnwick Castle. The valley floor of the Aln sits at about 44 metres. The hill commanded a panorama before anyone built anything on it. Before the tower, a fire beacon stood here to warn the surrounding country of approaching enemies, a Scots raiding party or a Northumbrian rebellion or whichever direction the threat was coming from that century. Robert Adam, the most fashionable British architect of the late eighteenth century, designed the tower in an elaborate Gothic Revival style. He worked together with his brother John on other Percy commissions including the interiors of Northumberland House in London and Syon House on the Thames. At Alnwick, however, the brief was theatrical: build something tall, build something ornamental, build something that would catch the light from miles away and remind every passing landowner whose park this was.

The tower has six stages of dressed stone, rising 26 metres above the hilltop. A verandah runs around the lowest stage. A projecting balcony crowns the top. Above the balcony sits a cast-iron fire basket, an architectural nod to the older beacon that had once warned the country of trouble. Four small rectangular buttresses break the circular plan. An internal newel staircase, lit by windows, climbs the height of the tower. From the top balcony the view sweeps west across the vale of Whittingham, north to the Cheviot and the Scottish hills, north-east to Hulne Priory inside the park walls, and east across the coastal plain to the North Sea. The castles at Bamburgh and Dunstanburgh and Warkworth all show. The Farne Islands and Coquet Island both show. The only direction that the tower does not command is south, where Alnwick Moor rises higher and blocks the view back over Alnwick itself.

Thomas Percy, the antiquary who later became Bishop of Dromore, recorded in a letter from 1765 that the Duke had been planning a tower on Brizlee Hill twelve years before construction began. The plans took shape slowly. Lady Elizabeth died in 1776. Adam designed the tower the following year. The masons finished in 1781. The architectural historian J. Mordaunt Crook, in his Alfred Bossom lecture on Northumbrian Gothick, treated the tower as a memorial that had been hidden in plain sight. From most angles the building looks like a folly built for the sheer pleasure of building it. It is something rarer than that. It is a widower's monument to a marriage that brought him the dukedom in the first place, since the Percy title had passed through the female line, and Hugh Percy was Duke only because Elizabeth had been a Percy heiress. He built her, in stone and Gothic ornament, a way of looking at the country she had given him.

The tower stands inside Hulne Park, which the Duke of Northumberland opens to walkers during daylight hours but closes at night. Reaching it on foot is straightforward: a marked footpath climbs from the lodge gates near the town, leading through Capability Brown's parkland past Hulne Priory and up onto the hill. The path is about four miles round trip from the town centre and rises gradually, so most walkers manage it without difficulty. The tower itself is not generally open to visitors, although the estate has occasionally given guided tours of the interior. Most visitors simply stand at the base, look up at six storeys of yellow sandstone catching the afternoon light, walk around it once, and look back at the view that the Duke wanted everyone to see.