From Halopedia, the Halo wiki
Two types of gondolas were encountered on Installation 05, the first over the lake near the Temple ("Temple gondolas"), and the second near the Library (the "Library gondolas"). The smaller Temple gondolas and underwater elevators are the only way to reach the Forerunner temple where the Prophet of Regret initially set up his base of operations during the Battle of Installation 05. These gondolas are supported by anti-gravity "tethers" below and above. The larger Library gondolas and the teleportation grid are the only way to reach Installation 05's Library.
Installation 07 also possessed one type of gondola transit system. One of these vehicles transported Chakas, Vinnevra, Riser and Mara from the Halo's Lifeworker Central to Mendicant Bias' core facility deep underneath the ringworld's surface. This transport was the shape of a pair of long and sleek curves — similar in shape to boomerangs — whose tips linked to form the vehicle's bow and stern. A ramp extended from the craft to allow entry. Unlike the partially exposed interiors of the gondolas on Installation 05, this gondola had an enclosed interior, the walls of which could become transparent or opaque at will. Because of the otherworldly Forerunner technologies they had previously witnessed, the humans aboard the gondola considered the vehicle surprisingly primitive and wondered if it was actually part of an elaborate playground built for Forerunner children.
Following a predetermined course over a variety of water bodies and occasionally skipping over obstacles in the landscape, the trip took several hours. At the end of the surface journey, the ferry dove into an enormous gap in the installation's landscape, around 20-30 kilometers in diameter. Several massive waterfalls cascaded down the circular opening, turning into controlled, braided streams further below. The gondola descended down the pit in freefall for a significant amount of time before coming to rest in Mendicant Bias' lair, the floor of which was covered in a green-glowing maze of hard light paths resembling a spiderweb, with the transport settling in the center and prompting its occupants to exit by extending its ramp.
Another type of gondola was encountered on the Forerunner shield world Requiem, inside a communications tower that was being used as part of a traffic control system by the Didact. The gondola was used to traverse a large chasm between the tower entrance and the carrier wave generator. Users must traverse a small light bridge to enter the gondola. System overrides found on two separate structures within the tower could be used to halt the gondola's progress. These structures were also connected to the gondola by light bridges.
The Temple gondolas are traveled upon in the level Regret, in Halo 2. It can be started by the player character Master Chief, using its switch. It cannot be stopped manually, though it automatically stops when docking to either boarding platform. The gondola also stops momentarily when passing a gondola moving in the opposite direction. A glitch known as the "Gondola Grunt" exists, wherein trapping a Grunt on the second Gondola will cause its AI to dramatically change tactics and personalities.
The Library gondola is traveled upon in the level Quarantine Zone, in Halo 2. It is started automatically by the player character Arbiter, in a cutscene. It automatically stops when docking to either docking station.
In the Halo 4 level Shutdown, the gondola is activated from a switch on the gondola but is twice stopped remotely from two structures adjacent to the gondola's path. The first is guarded by Covenant and the second by several Promethean Knights. It is stated by Cortana that the Didact gave the Covenant access to the system overrides in order to slow the Spartan's progress. A Forerunner weapons cache can be found on the lower level of the gondola, which can be of great usefulness in combating the enemy.
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