From Terry Pratchett's Making Money:
"How did you find out they were down there?"
"The usual way. One of our golems heard one singing. Imagine that. It's been underground for sixty thousand years..."
In the night under the world, in the pressure of the depth, in the crushing of the dark...a golem sang. There were no words. The song was older than words; it was older than tongues. It was the call of the common clay, and it carried for miles. It traveled along fault lines, made crystals sing in harmony in dark, unmeasured caverns, followed rivers that never saw the sun...
...and out of the ground and up the legs of a golem from the Golem Trust, who was pulling a wagon loaded with coal along the region's one road. When he arrived in Ankh-Morpork, he told the Trust. That was what the Trust did: it found golems.