In Titus Alone Titus leaves Gormenghast and travels in what seems to be a setting similar to the modern world.
The title of Earl indicates a British setting and all the personal and place names indicate a European cultural setting. If Gomerghast is located in China it would be in a millennia-old European enclave that would be another aspect that makes it a fantasy novel.
Added Aug.5-6, 2023.
Mervyn Peake was born in China in 1911. HIs family returned to England in 1914, and then went back to China from 1916 to 1922. So Peake had childhood memories of life in both China and England.
Another boy who lived in China about that time was Puyi (1906-1967), a member of the Aisin-Gioro clan, the Qing Dynasty. He was selected to be Emperor at the age of 2 in 1908, meaning adults ruled while he tok part in ceremonies. As emperor he lived in the walled Purple Forbidden City in Beijing and in the nearby Summer Palace in the country.
The Qing Dynasty was overthrown and the Republic of China established in 1912. But Puyi and the court continued to live in the Forbidden City and to perform imperial rituals, now rather meaningless. In 1917 a warlord loyal to the Qing captured Beijing and Puyi was proclaimed emperor again from July 1 to July 12. And in 1924 Puyi was expelled from the Forbidden City.
And Peake was probably somewhat aware of the life of the older boy Puyi in the Forbidden City, who was the nominal ruler but with adults in charge, and with everyone spending their time on various ceremonies.
The Forbidden City is listed as number 5 in the list of largest palaces in the world. The walls enclose an area of 720,000 square meters or 180 acres. The buildings within the walls have a total floor space of 150,000 square meters or 1,614,587 square feet.
Unfortunately, none of the five larger palaces on the list was likely to have had a child monarch dwelling there when they were at their largest.
The Apostolic Palace in the Vatican has never had a child ruler. The Istana Nurul Iman in Brunei was completed as recently as 1984.
Louis XIII, Louis IV, and Louis XV may have lived in the now destroyed Tuileries Palace, which was eventually connected to the Louvre, as child rulers. But the Louvre didn't reach its maximum size until later in the reign of Napoleon III.
And the largest palace listed, the Hoffburg in Vienna had no child monarchs. Emperor Leopold I was still 16 when he inherited Austria, Hungary, and Bohemia, and Franz Joseph was 18 when he came to the throne.
However, some now destroyed palaces were quite large. Some of the Caliphal palaces at Samarra north of Baghdad were rather similar in size to the Forbidden City.
In 200 BC, the Weiyang Palace was built at the request of the Emperor Gaozu of Han, under the supervision of his prime minister, Xiao He. The palace survived until the Tang dynasty, when it was burnt down by marauding invaders en route to the Tang capital, Chang'an. It was the largest palace complex ever built on Earth,[22] covering 4.8 square kilometres (1.9 sq mi), which is 6.7 times the size of the current Forbidden City, or 11 times the size of the Vatican City.
The Daming Palace was the imperial palace complex of the Tang dynasty in Chang'an. It served as the imperial residence of the Tang emperors for more than 220 years. In 634, the Emperor Taizong of Tang launched the construction of the Daming Palace at Longshou Plateau. He ordered the construction of the summer palace for his retired father, the Emperor Gaozu of Tang, as an act of filial piety. However, the Emperor Gaozu grew ill and never witnessed the palace's completion before his death in 635, and construction halted thereafter. Wu Zetian commissioned the court architect Yan Liben to design the palace in 660, and construction commenced once again in 662. In 663, the construction of the palace was completed under the reign of the Emperor Gaozong of Tang. The Emperor Gaozong had launched the extension of the palace with the construction of the Hanyuan Hall in 662, which was finished in 663. On 5 June 663, the Tang imperial family began to relocate from the Taiji Palace into the yet to be completed Daming Palace, which became the new seat of the imperial court and political center of the empire. The area of the palace complex was 3.11 km2.
https://en.wikipedia.org/wiki/List_of_largest_palaces#Largest_former_palace_complexes
So there should have been a number of child monarchs who reigned in the Weiyang and Daming palaces.
In the medieval Japanese capital Kyoto, the greater palace or Daidairi occupied more than a square kilometer. The imperial residence called the Dairi or inner palace was a much smaller walled enclosure within the Daidairi.
The Daidairi was a walled rectangular area extending approximately 1.4 kilometres (0.87 mi) from north to south between the first and second major east–west avenues Ichijō ōji (一条大路) and Nijō ōji (二条大路) and 1.2 kilometres (0.75 mi) from west to east between the Nishi Ōmiya ōji (西大宮大路) and Ōmiya ōji (大宮大路) north-south avenues.[29][30] The three main structures within the Greater Palace were the Official Compound (朝堂院, Chōdō-in), the Reception Compound (豊楽院, Buraku-in) and the Inner Palace (内裏, Dairi).
https://en.wikipedia.org/wiki/Heian_Palace
In medieval Japan it was very common for a young child to be selected as emperor, to reign for a few years performing imperial ceremonies, and to abdicate to become a retired emperor and one of the leading members of the court. So if Mervyn Peake knew anything about medieval Japanese history he would have known that many child monarchs lived in the vast imperial palace complex.
From 1642 until 1705 and from 1750 to the 1950s, the Dalai Lamas or their regents headed the Tibetan government (or Ganden Phodrang) in Lhasa, which governed all or most of the Tibetan Plateau with varying degrees of autonomy.[9]
https://en.wikipedia.org/wiki/Dalai_Lama
And the Dalai lamas were usually selected as children believed to be reincarnations of earlier Dali Lamas. The seat of the Dali Lama's administration was the Potala Palace at Lhasa.
the Great Palace at Constantinople was the center of imperial administration from 330 to 1204, and the main imperial residence until about 1000.
The total surface area of the Great Palace exceeded 200,000 square feet (19,000 m2).
https://en.wikipedia.org/wiki/Great_Palace_of_Constantinople#Description
Naturally a number of Child emperors reigned in the Great Palace. One of the youngest was Constantine VII, call Porphyrgenitus because he was born in the Purple, the Purple Chamber of the palace. He was born 17/18 May 905. When he was 2 years old the Emperors Leo VI and Alexander had Constantine made junior co emperor on 15 May 908. Leo VI died 11 May 912 and Alexander died 6 June 913, leaving Constantine VI the senior emperor with a regency council. Constantine VI I didn't get to rule until 945 to 959.
Constantine VI was a prolific writer, and one of his most important works was a book about the imperial ceremonies in the palace. So if any child emperor in the Great Palace was any inspiration for Titus Groan, Earl of the vast castle of Gormenghast, Constantine VII would be the one.
The Great Palace at Constantinople was very small compared to the Forbidden city, but was built of stone, bricks, concrete, and mortar instead of wood, and so would more nearly fit the European style descriptions of Gormenghast.
A few residence in the United Kingdom have been suggested as possible inspirations for Gormenghast.
There is Blenheim Palace, residence of the Duke of Marlboro, with its vast size and strange baroque shapes.
Another candidate is Knole, a rather more normal looking but quite vast mansion.
Knole (/noʊl/) is a country house and former archbishop's palace owned by the National Trust. It is situated within Knole Park, a 1,000-acre (400-hectare) park located immediately to the south-east of Sevenoaks in west Kent. The house ranks in the top five of England's largest houses, under any measure used, occupying a total of four acres.1
https://en.wikipedia.org/wiki/Knole#
I believe that Gormenghast is described in one passage as being cross shaped, with a central tower. And so I wonder if it was inspired by William Beckford's legendary Fonthill Abbey.
Anyway, the above suggestions are merely suggestions about what places might have inspired Gormenghast.
Gormenghast is not in any real region, but in the imagination of Mervyn Peake. As some have said before, Gormenghast should be in the Peak(e) District, but it is unknown which country or continent includes the Peak(e) district.