From Destinypedia, the Destiny wiki
The Relic is an artifact that appeared on Mars after the planet was returned from the period it spent shrouded in darkness by the Black Fleet. Described as a "resonance engine," it is capable of reaching across time to recreate objects based on memories, and to impart visions of the past associated with an object. It is the location where players can engage in Weapon Crafting.
The Relic was first discovered by The Hidden in their first exploration of the returned Mars. They set up The Enclave outside and called Ikora Rey and Eris Morn to conduct a survey over the artifact. As Eris exited the building though, they were interrupted by the arrival of the Imperial Cabal and The Lure.
Later on, after The Guardian was rescued from the Court of Savathûn and brought to the Enclave, Ikora directed them to explore the Relic, specifically the Crafting Station, where they first unlocked the power of Deepsight, which allowed them to first craft The Enigma from the Artifact of the Black Fleet they previously acquired on Savathun's ship. They would subsequently return to craft more weapons.
After the Vanguard discovered how the Witch Queen was risen, Ikora used the Relic to pull out the memories recorded into Savathûn's petrified Worm, discovering how the Hive were tricked into embracing the Darkness.
The Relic is clearly of the same craftsmanship as the Pyramids, being made primarily of polished blocks of what appears to be black and white stone. It is partially built into the cliffside, where a large wall of black stone is visible as the only hint to its presence. A flight of stairs brings one to a large black stone door, which slides open on approach. The main chamber's structure is built out of the same black stone, and the walls are lined with molds of many items carved into rectangular blocks of many colored stones. In the middle of the room is the Crafting Station. This large table is also covered in item molds, and at its center is a spinning quadrilateral shape. From the vaulted ceiling a pendulum swings, always intersecting perfectly with the holes in the spinning shape on the table. A conduit comes out of the left side of the table, occasionally dispensing items of the Pyramids. Proceeding further in brings one down another flight of stairs, to an area in the underground of Mars, where several discs float in the air, which can be used as a firing range.