Voyager

Carl Sagan and Ann Druyan wrote:

In the annals of exploration, the achievements of the two Voyager spacecraft are unprecedented. The piddling journeys of Columbus and Magellan spanned a few tens of thousands of miles on the watery surface of one small world. Voyagers 1 and 2 have traveled billions of miles through the ocean of space, exploring dozens of new worlds along the way and revolutionizing our knowledge of the solar system in which we live. And as a gift of the brilliant mission design, these robot ships are no longer bound by the Sun's gravity. They have passed the outermost planets and are on their way to the cold, dark near-vacuum that constitutes interstellar space. Nothing can stop them. Their radio transmitters are unlikely to work beyond the year 2020. Thereafter, they will wander silently and forever in the realm of the stars.

Who knows who's out there? Perhaps the rest of the Milky Way Galaxy is populated by desolate, wasteland worlds circling a hundred billion stars. Or maybe the Galaxy is rich in life forms and intelligence and technology much further beyond our reach than the Voyagers are beyond the reach of Columbus and Magellan. Someday - maybe millions of years in the future - one of these ghostly, derelict ships may be detected and captured by the representatives of some devastatingly advanced interstellar culture. They will wonder about the shipbuilders.

If you could send a long message to such extraterrestrial beings - words, pictures, sounds, music - what would you say? How would you describe us? What would you leave out? Could you communicate intelligibly to very different beings with a wholly independent evolution? In 1977, at NASA's behest, a few of us had a remarkable opportunity to attempt such a (one-way) communication.

You can see what was recorded in that golden disc here. This is the golden disc cover:
This is the information on the cover:
You can find a detaild explanation of it here. You can read about its content here.