What is Dejima?
Dejima is an artificial island off the coast of Nagasaki. During Japan’s “closed period,” or sakoku, Dejima was Japan’s only allowed contact with the rest of the world, as this island was home to first Portuguese traders and then Dutch merchants. These merchants were only allowed on Dejima and were not able to go into Nagasaki. Japanese merchants and travelers were also not allowed onto Dejima unless they were specifically allowed entry for their job.
In 1951, the city of Nagasaki began restoration plans for Dejima and officially started the project in 1996. You can see the process of the restoration here, and browse the rest of the website for more information on the history of Dejima, its buildings and purpose.
History of Dejima
The shogun Iemitsu ordered the construction of the artificial island in 1634, to accommodate the Portuguese traders living in Nagasaki and prevent the propagation of their religion. But after an uprising of the predominantly Christian population in the Shimabara-Amakusa region, the Tokugawa government decided to expel all Western nationals except the Dutch employees of the Dutch East India Company (Vereenigde Oostindische Compagnie, VOC).
Since 1609, the Dutch had run a trading post on the island of Hirado. For 33 years they were allowed to trade relatively freely. At its maximum the Hirado trading post covered a large area.[quantify] In 1637 and 1639 stone warehouses were constructed within the ambit of this Hirado trading post. Christian-era year dates were used on the stonework of the new warehouses and these were used in 1640 as a pretext to demolish the buildings and relocate the trading post to Nagasaki.
In 1639, the last Portuguese were expelled from Japan. Dejima had become a failed investment and without the annual trading with Portuguese ships from Macau, the economy of Nagasaki suffered greatly. Thanks to their restrained but versatile policies and to their hostility to Spain and Portugal – which had both a religious and a political basis – the Dutch alone succeeded in being exempted from expulsion, but they were forced by government officials to move from Hirado to Dejima.
From 1641 on, only Chinese and Dutch ships were allowed to come to Japan, and Nagasaki harbor was the only harbor to which their entry was permitted.
Photos of Old & Current Dejima
A model reconstruction of old Dejima.
The Thousand Autumns of Jacob de Zoet
In 2010, author David Mitchell published a novel called The Thousand Autumns of Jacob de Zoet, which is primarily about a Dutch merchant who is based on Dejima.
Mitchell spent four years working on the novel, researching and crafting a vision of 18th century Japan. Small details, such as if people used shaving cream or not, could use up lots of time so that a single sentence could take half a day to write. “It was tough,” Mitchell said. “It almost finished me off before I finished it off.” 
The origins of the novel can be found in 1994 when Mitchell was backpacking in western Japan while on a teaching trip. He had been looking for a cheap lunch in Nagasaki and came upon the Dejima museum. “I never did get the lunch that day,” Mitchell said, “but I filled a notebook with information about this place I’d never heard of and resolved one day to write about it.”
Some of the events depicted in the novel are based on real history, such as the HMS Phaeton’s bombardment of Dejima and subsequent ritual suicide of Nagasaki’s Magistrate Matsudaira. The main character, Jacob de Zoet, bears some resemblance to the real-life Hendrik Doeff, who wrote a memoir about his time in Dejima.
Late in the book, “land of a thousand autumns” is described as one of the names used by the Japanese for Japan. There is a Japanese saying 一日千秋, literally “a thousand autumns in one day”, which means “waiting impatiently for something.”