The Werther Box was an enchanted vault created by the former member of the Men of Letters, Cuthbert Sinclair. It was created to hold a special codex stolen from the Grand Coven witch Nadia, and ensure that the codex does not fall into the Coven's hands again. However, the warding spell was too powerful and far beyond Men of Letters handling, making it too dangerous and caused two Men of Letters death. It was also the reason for Cuthbert's expulsion.
The Werther Box came with a "security system" wherein anyone who attempted to open it, without doing the proper ritual first, was struck with a spell that led to the person killing themselves. The warding spell was so potent that it reached a theoretical rate of 98% lethality. The only way to turn off the protection spell was to use a large amount of blood from a member of the Men of Letters.
In 1973, 17 years after Cuthbert's expulsion (15 years after the Men of Letters Downfall), a girl, Suzie, found the box in her house (which, unknown to her and her family, was an ex-Men of Letters chapter house) in St. Louis and accidentally activated it, causing her entire family to commit suicide. She survived, but suffered serious trauma and became a recluse, making her social skills "rusty".
In 2015, Sam learned about its presence and wanted to retrieve it so he could obtain the Nadia's Codex. With Dean's help, they nearly make it but Suzie learns their intentions, and makes Sam's spell breaking ritual fail, and the Werther Box's curse is released once more. On this occasion, it caused Suzie's death and pulled Dean into his near death experience. It nearly caused Sam to commit suicide (by manifesting Suzie's apparition), but Rowena came and saved him via a spell
Later, based from its inscription (thanks to Rowena assist), they learned how to turn off the box. Sam sacrificed himself in order to turn off the box. But the amount of his blood was not enough. Dean (with the assist of the Mark of Cain's power) capable of overpowering the spell and able to escape from its influence. He later added his own blood to complete the ritual so they can turn off the box.
It was smashed into scrap metal by Dean Winchester just to be sure.