"Field Trip" is the twenty-first episode of the sixth season of the science fiction television series The X-Files.

The episode was written by John Shiban and Vince Gilligan, from a story by Frank Spotnitz, and was directed by Kim Manners.

The show centers on FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) who work on cases linked to the paranormal, called X-Files.

What they discover is a giant fungal growth that causes the agents to have two separate hallucinogenic episodes, which eventually merge into one shared hallucination.

In order to prepare for the episode, various information on mushrooms, fungi, human decomposition, and cave geology was researched by the series' crew members.

In Boone, North Carolina, Wallace (David Denman) and Angela Schiff (Robyn Lively) return home after a day out hiking in the fields.

Angela and Wallace head off to bed in one another's arms but as the camera pans out the scene shifts to their skeletal remains in the same position in the middle of a field.

Mulder, believing that bodies are a result of the famous Brown Mountain Lights, heads out to the scene of the discovery while Scully stays behind with the coroner (Jim Beaver) to perform more tests.

Meanwhile, Scully has discovered that the yellow substance mainly consists of organic material found in digestive juices, although it appears plant-like.

Back at the coroner's office, Scully identifies Mulder's remains from his dental records but finds no evidence of the secretion on the skeleton.

As Mulder and Scully discuss what has happened, they both begin to realize that they are still in the cave being digested by the substance while they are comatose; somehow, they are sharing the same hallucination.

As the realization occurs, they both awaken, deep in the cave and Mulder fights his way out of the ground dragging Scully behind him to safety.

Later, in Walter Skinner's (Mitch Pileggi) office, Mulder begins to doubt once more that they are free at all, asking Scully to name any sort of drug that causes its effects to halt once users know they are hallucinating.

Scully is in disbelief until Mulder proves his point by shooting Skinner in the chest; the yellow substance oozes out of the bullet wounds.

Mulder sticks his hand through the earth ceiling as Skinner and a team of rescue staff manage to locate them and drag them out and haul them to the safety of an ambulance.

[3] Spotnitz called the episode a "wonderful mind game" but was worried that the convoluted story and pace would confuse the viewer.

[4] Special effects coordinator John Vulich was tasked with designing "spidery, eight-foot tall" fiberglass mushrooms.

[4] The art department consulted various geological text books to properly create the stalagmites and stalactites for the cave scenes.

[4] The opening to the cave was filmed at Bronson Canyon, most notable for being the location of Bruce Wayne's Batcave in the Batman television series that aired in the 1960s.

Anderson and Duchovny were literally buried under the earth for the final scene, with the actors donning wet suits and being covered in the vegetable fluid and soil.

"[18] Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, rated the episode five stars out of five.

[19] Furthermore, however, Shearman and Pearson noted that, "[the episode is] not merely poking fun at the conventions of the long running sci-fi show, but inviting its audience to question the truths around us we take for granted".

Connie Ogle from PopMatters ranked the "giant underground mushroom thingie" among the "best" monster-of-the-week, describing it as "too crafty to end up on a pizza".

Cyriaque Lamar from i09 called the mushroom one of "The 10 Most Ridiculous X-Files Monsters" and wrote, "Mulder and Scully conquer this mycological nightmare by jointly fighting it during a drug trip — some real astral plane shit, brah.