Located near Fairlie in North Ayrshire and the seat since the mid-17th century of the Earls of Glasgow, Kelburn Castle’s exact age isn’t known. The best guess puts its foundation at the mid-12th century. It is certainly old enough to have been standing during the Battle of Largs in 1263, a pivotal moment in Scottish history which helped throw off centuries of invasion by Norse raiders when the Scots army led by Alexander III bested the Norwegian forces of Haakon Haakonsson. The Treaty of Perth followed three years later, effectively handing control of the Hebrides to Scotland.

The first Earl of Glasgow was David Boyle, who assumed the title on its creation in 1703. He added the castle’s north-west wing. The 6th Earl, George Boyle, added the north-east wing. When his son was made Governor of New Zealand in 1892, he commemorated the castle by lending its name to the town of Kelburn, now a suburb of Wellington. Today’s incumbent, the 82-year-old, Eton-educated 10th Earl Patrick Boyle, occupies himself closer to home – when not in residence at Kelburn he sits as a Liberal Democrat peer in the House of Lords.

But what’s most notable eye-catching about the castle is not its wings, its gardens or the yurts available to hire in its grounds – it’s the huge, colourful graffiti mural which covers the 16th century tower house on the castle’s south side. The artwork dates from 2007, when the present Earl invited four Brazilian graffiti artists to spend a month at the castle and, in collaboration with local graffiti artists, decorate it in their own inimitable style.

The Brazilians were Francisco Rodrigues da Silva, known as Nunca (‘Never’ in Portuguese); identical twin graffiti team Otavio and Gustavo Pandolfo, who work under the name Os Gemeos; and Otavio’s wife, Nina Pandolfo. Collectively they have worked on street murals on Los Angeles, Lisbon, Berlin and beyond, and featured in the Tate Modern’s 2008 Street Art exhibition. None of them had every spray-painted an 800-year-old castle before, however. The Kelburn mural was intended to be only temporary – thankfully, it has now become permanent. In 2011, stencil and graffiti art expert Tristan Manco listed it as one of the top 10 best examples of street art anywhere in the world. Truly a modern wonder.