Dejima was (and has since been reconstructed) as an artificial island built using reclaimed land from the port of Nagasaki. It was used to quarantine foreign traders (Portuguese, then Dutch) during the Edo period of the Tokugawa Shogunate. Later on, it was integrated into Nagasaki through land reclamation and became land-locked and the original boundaries completely obscured.
More recently, extensive restoration works have tried to recreate the original island and restore or rebuild the original buildings. When we visited, we were impressed by the amount of work done. There is a mini-Dejima scale model of the island so we can have a good understanding of what the island looked like during it’s heyday, and the current version contains many of the same elements. Many of the buildings were open and are effectively museums containing many artefacts from the trading history of Nagasaki.
All in all, I really enjoyed the visit.