The portal was created by Philip Wittebane, the first human to live on The Boiling Isles. It uses titan's blood as a power source, which is a rare substance that causes leaks between realms. The key is also filled with titan's blood and without it the door will not open. Even fabricating a new key would not open the portal if the original went missing.
Sometime after Philip's disappearance, the portal and its key ended up buried in the earth next to the Clawthorne residence partially submerged in the ground. When Eda was a teenager, she discovered the portal while running away from home after contracting the Owl Curse. She found it peeking out of the ground. After discovering it could open a gateway to the human realm, she used it to escape her mother, who was ardent in removing the curse. Over the next thirty years, Eda used the portal to either hide from her mother or collect human artifacts and sell them on her Human Collectibles stand.
Emperor Belos was also aware of the portal's existence. In order to obtain it, he demanded Luz turn it over in exchange for Eda's safety, and Luz did so, but the portal was subsequently destroyed by her Fire Glyph. Nonetheless, Belos was able to salvage the centerpiece and rebuild it as part of a larger mechanism within his castle. However, Belos could not get the portal to work without the key, which was still in Luz's possession. By "Eclipse Lake", they key was in Amity's possession while Luz was sick with the common mold. When Hunter realized she had the key, he tried to take it from her. But after a rentless fight between the two, Amity reluctantly surrendered the key when Hunter threatened to harm Luz is she did not. But, before handing it over, Amity crushed the key in her hand, causing it to leak titan's blood on her hand, collecting the primary ingredient for Luz's plan to return home.
When dormant, it resembles a brown attaché case with a large, yellow, slit pupil eye on one side. When activated, the portal unfolds to the dimensions of a standard doorway. The door can then be opened, connecting the two realms and allowing passage between them. While the demon realm side of the portal is portable and can be opened anywhere, the earth realm side of the portal appears to be fixed to an abandoned house behind the home of Luz Noceda.
Based on Philip Wittebane's designs, the inner workings of the portal is a mix of human tech combined with magic and organic based components.