Synopsis

After the discovery of a massive underground ecosystem beneath a ruined Romanian abbey, a team of scientists and professional cave divers descends into the unexplored network. A collapse traps them far below the surface, where they encounter an aggressive species that has evolved in total darkness. As supplies and escape routes disappear, the survivors must navigate flooded passages and hostile creatures to reach daylight.

Factoids & Trivia

• The production filmed mainly in Romania, including Bucharest, Transylvania, and the area around Zarnesti. Underwater sequences were also shot at Hidden Worlds Cenote Park in Quintana Roo, Mexico.

• A 750,000-gallon tank was constructed specifically for the underwater photography.

• Professional cave divers were hired as consultants to improve the technical credibility of the diving equipment, procedures, and underwater exploration scenes.

• The film drew inspiration from the discovery of unusual cave ecosystems, particularly Romania's Movile Cave. Scientists found numerous previously unknown species there, although nothing comparable in size to the movie's creatures.

• Creature and special makeup effects were designed and fabricated under the supervision of Patrick Tatopoulos, with additional visual effects by Luma Pictures.

• The tattoo reading "V.S.S.F." refers to the Swiss Society of Explosive Engineers, matching the character's work with explosives.

• The film arrived during a brief 2005 cycle of cave-horror releases that also included the British film "The Descent" and the similarly titled "The Cavern."

• Lakeshore Records released two soundtrack albums: one containing the orchestral score and another built around heavy metal tracks. Nightwish's "Nemo" plays over the end credits.