In Star Wars: Episode I - The Phantom Menace, Obi Wan fights with Darth Maul on the planet Naboo in Queen Amidala's castle and kills Darth Maul. After his death, Darth Maul fell down a shaft. What is the tunnel called?
While fans typically refer to it as a "reactor shaft", more official materials refer to it differently.
According to the script for the movie Star Wars Episode 1: The Phantom Menace, where this event takes place, it is the melting pit connected to the power generator.
INT. THEED - POWER GENERATOR - MELTING PIT
OBI-WAN screams as the pulsing electron gate opens, and the SITH LORD attacks him. The DARK LORD is relentless in his assault on the young JEDI. OBI-WAN and DARTH MAUL use the Force to fling objects at each other as they fight. DARTH MAUL seems to have the upper hand as OBI-WAN grows weary. DARTH MAUL catches OBI-WAN off guard, and the JEDI slips into a melting pit. He is barely able to hold onto a nozzle on the side of the pit. DARTH MAUL grin evilly at OBI-WAN as he kicks OBI-WAN's lightsaber down the endless shaft.
The SITH LORD smiles as he goes in for the kill. At the last moment, OBI-WAN jumps up out of the pit, calls QUI-GON's lightsaber to hi, throwing DARTH MAUL off. The young JEDI swings with a vengeance, cutting the SITH down. DARTH MAUL falls into the melting pit to his death. OBI-WAN rushes over to QUI-GON, who is dying.
StarWars.com also calls it a "melting pit" in its page for the Reactor Core Duel.
On Naboo, Qui-Gon and Obi-Wan team up to defeat Darth Maul in a lightsaber duel. After cutting Qui-Gon down, Maul faces off with Obi-Wan, who defeats the Sith Lord by sending his bisected body into a deep melting pit.