Control room

Summary
Halo's Control Room is a temple-looking structure where the Index is used to activate the Halo's weapon. It is unknown if there are only two designs, which are replicated in the other Halos' Control Rooms, or each Control Room has its individual designs, due to lack of information on the other Halos.

Control Room, Installation 04
In Halo: Combat Evolved, the Control Room for Installation 04 was found in the stages Assault on the Control Room and Two Betrayals. The main console was found behind a set of doors with connecting corridors. It has been noted that when viewed from the top, the main console room resembles the Marathon logo. The large, cylander shaped room features a massive hologram of Halo, and the planet Threshold in its center. Suspended in the air is a large circular catwalk around the planet. There are no other control stations save for the main control console. The Master Chief reached the main console and inserted Cortana, who sent him to the next level, 343 Guilty Spark to attempt to stop Captain Keyes from unleashing the Flood. He returned to the Control Room at the start of Two Betrayals to insert the Index as prompted by 343 Guilty Spark, but was stopped by Cortana. 343 Guilty Spark sent Sentinels to stop the Chief. After the Chief destroyed the Sentinels, he took Cortana and left. The Control Room was presumably untouched from then on until Installation 04 was destroyed.

Control Room, Installation 05
In Halo 2, the Control Room is on an island in a sea, seen for the first and last time in The Great Journey. It is there that Tartarus brought Miranda Keyes to the Control Room along with 343 Guilty Spark to attempt to activate Delta Halo. He succeeded in starting it up, but was slain by the Arbiter and Sergeant Johnson and had the Index removed by Miranda before the weapon could fire.