The Observatory was a room in Olmec's Temple. This particular room went through the most incarnations during the show; three different objectives were housed in the Observatory.
Sundial (Layouts I-VII)
When a player entered the Observatory, they would had to spin the sundial to open a door.
Celestial Lights (Layouts VIII-IX)
When a player entered the Observatory, they had to spin the celestial lights (a small canister from which light emanated through small holes). This lowered the lights in the room, sent the celestial lights into perpetual motion, and opened a door.
Stone Column (Layouts X-XIV)
For the entire second season, when a player entered the Observatory, they had to put together the puzzle on the stone column to open a door. Furthermore, where Season 1 had a door leading to the left blocked by a metal rod (that was sometimes manually opened to no avail, such as in The Snake Bracelet of Cleopatra), Season 2 featured a thick slab that lowered.