A 31st-century device kept by the time agent Daniels in his quarters aboard Enterprise, which projects a navigable holographic map of history, shown to Archer in Cold Front.
The Temporal Observatory is a small piece of future technology belonging to Daniels, an operative from the 31st century who poses as a crewman aboard Enterprise NX-01. When activated it fills the room with a three-dimensional display of events across time, allowing the user to examine the timeline.
It appears in the first-season Enterprise episode Cold Front. Daniels reveals his true identity to Archer, uses the device to explain the Temporal Cold War, and asks for help in capturing the Suliban agent Silik, who is also aboard.
After Daniels is apparently killed, Archer has his quarters sealed with the equipment inside. The crew return to that store of future knowledge on later occasions when the Temporal Cold War touches the ship again.