A Hellmouth was an area in which the barriers between dimensions was particularly weak, allowing the creation of portals between Earth and several hell dimensions. For these reasons, the Hellmouth attracted demons and other supernatural creatures, becoming a "hot spot" for supernatural activity. Distortions of the laws of physics were made possible by the Hellmouth's influence, such as Billy Palmer's nightmares intruding into reality and the ignored Marcie Ross becoming invisible, as well as various acts of super-science, including the reanimation of Daryl Epps, the chemical transformations of the Sunnydale High Swim Team and Pete Clarner, and the creation of robots Ted and April.

The Sunnydale Hellmouth lies underneath the library of Sunnydale High school. The Seal of Danzalthar is the gateway, under the library in the old school and below the principal's office in the new school. There have been many attempts by apocalyptic individuals/groups to open or utilise the Sunnydale Hellmouth, such as in the episodes "The Harvest", "The Zeppo" and "Doomed". In season 7, The First Evil was going to open it to bring forth the Turok-Han, but Buffy and the Potential Slayers descend through the portal in the series finale, "Chosen" to fight them. Spike uses a magical amulet to destroy the Turok-Han (as well as himself) and close the Hellmouth. The ensuing cataclysm not only collapses the Hellmouth, but swallows the entire town of Sunnydale along with it. As spring 2003, the Sunnydale Hellmouth is permanently closed and inactive.

Known Hellmouth locations

• Sunnydale, California
• Cleveland, Ohio
• Los Angeles, California (artificial mini-Hellmouth, destroyed)

Etymology

The word "Hellmouth" is derived from the original, Spanish name for Sunnydale: Boca del Infierno, translated as "Mouth of Hell." While in this instance it refers to the city as a whole, in the Scoobies' usage, it has come to refer to the center of this mystical convergence.

Attempts at Opening the Hellmouth

• First attempt by The Master in which he becomes "stuck" in it. Takes place some time before the events of the series.
• Opening by The Master | "Prophecy Girl"
• Opening by the Sisterhood of Jhe | "The Zeppo"
• Ritual performed by three demons | "Doomed"
• Opening of the Seal of Danzalthar by the First Evil | "Never Leave Me"
• Second opening of the Seal of Danzalthar by Lissa | "First Date"
• Third opening of the seal of Danzalthar by Buffy, Faith and all the potential slayers | "Chosen"