They stretch across the ocean. They're three or five or eight thousand miles in length, and if the material science and the computational technology is incredibly complicated, the basic physical process is shockingly simple. Light goes in on one end of the ocean and comes out on the other, and it usually comes from a building called a landing station that's often tucked away inconspicuously in a little seaside neighborhood, and there are amplifiers that sit on the ocean floor that look kind of like bluefin tuna, and every 50 miles they amplify the signal, and since the rate of transmission