A haunting.

Sentient spirits have been acknowledged as part of the transcendental fabric of existence from before the dawn of the written word (for an example, see the Semien Mi'irabawi cave paintings). The creation of Walther gates in 1735 (ref. chapter 19, "Immanent-Transcendent Interaction") was the first step towards a scientific understanding of the underlying mechanics of hauntings. However, Samuel Walther was a devout Druid and uninterested in spirits. He applied his technique exclusively to ley nodes, creating the first rigorous theories of transcendental energy dynamics, but did not consider further applications of his revolutionary technology. Only a century later would Oscar Ortiz and Johannes Bauer's use of Walther gates in the Keller House reveal the true nature of hauntings.

Ortiz and Bauer were initially tasked with investigating an anomolous churel by the Wesen Ministry. The spirit matched nearly every classic criterion of a churel, but was uncharacteristically benevolent. In the course of their research into the entity, Ortiz and Bauer devised a primitive form of net-gating to envelop the entire property within a spiritually contiguous Walther gate. After erecting this impermeable barrier they were able to measure the spiritual dynamics of the property with an unprecedented level of accuracy. They quickly observed that their readings were inconsistent with the spiritual output of a churel and began to investigate the surplus transcendental energy.

This led to the discovery of a long-theorized but never observed phenomenon: the non-sentient haunting, or NSH. At some point prior to the formation of the churel, the Keller House became haunted with goodwill. Because the churel was formed under the conditions of this NSH, it lacked the malevolent **** associated with such spirits. This discovery gave rise to the field of modern phantasmatology. Today, phantasmatologists are able to create, alter, and remove NSHs at scale thanks to their pioneering work. The hauntings that keep temples silent, parks verdant, and hospitals sanitary are all a direct result of Ortiz, Bauer, and Walther's innovations.

-Introduction to the History of Transcendental Studies, Chapter 22: Phantasmatology