The Detragan (later called the "Detra-Gigant") is a giant machine designed and built by Jean Descole in Professor Layton and the Eternal Diva. While it only has a single organ keyboard, it is able to simulate an entire orchestra.
One year ago, prior to the movie, Oswald Whistler had the Detragan built to house Melina's memories, in the hope that he would be able to find someone who could contain them in his/her mind. Candidates would be wired up to the machine and have her memories pumped into their brains.
Almost everyone that Oswald used resisted the process, apart from Melina's friend Janice Quatlane. Oswald didn't know that the transfer had worked on Janice, and was growing desperate, as the Detragan could only hold Melina's memories for so long.
What Oswald didn't know was that Descole had double-crossed him, and only agreed to build the Detragan so he could raise the ruins of Ambrosia. When he appeared to have failed in this, the Detragan turned into a giant robot, the Detra-Gigant. It was soon destroyed after the ensuring fight between Professor Layton and Descole ended up in destroying the control panel, causing the machine to go out of control and fall off a nearby cliff into the ocean, being impaled by one of the tubes in the ruins of Ambrosia.