The Lantern is a magic lantern and an object in the episode "Incendium" of Adventure Time.
It was used as a containment device to protect the Flame Princess from burning through the Earth. According to Princess Bubblegum, she had the Flame King lock the Flame Princess in the lantern in order to prevent her from melting through planet and burning it if she were to experience romance due to her elemental matrix instability.
In "Earth & Water", the Flame Princess discovers that she is stronger than the Flame King and overthrows him by trapping him in the lantern he once trapped her inside of.
It is a giant lantern capable of holding Fire Elementals. The glass is a dark yellow with the base of the lantern being yellow with orange triangles. The base of the lantern has two knobs that are connected to ropes that suspend the lantern.