A thousand years ago, humans abandoned this city. Before they left they constructed the enormous cube shaped building that you know sits at the heart of the city, where all the roads come together. That building, as you are also aware, is a supercomputer composed of millions of nanoscale processors. This computer was programmed in secret by the human elders, given some task only they knew about but that would presumably take centuries to calculate.

Androids were left to maintain the computer as it delved for the secret they wanted and the humans left in silence. The city fell into ruins after a short time, only those areas necessary for the operation of the Cube were maintained by the caretakers.

Once a year the humans come back and gather around the cube. They ask it if it knows the answer yet, and always it tells them no.

Some years the humans arrive in throngs, but lately they are very few. I am here to tell you that the answer to the question was determined seconds after the humans asked it.