Power places were first discovered using dowsing rods, and are still used to find the ancient ley lines in the Earth. Because power sites would amplify energy, ancient priests/shamans would access that power in order to manifest crops or rain to feed their people. If you matched the energy, (like to like) then you will access the power of the place.
If you wanted fertile fields for growing crops, they would put a fertile woman in the field, or a father who had many children. The shaman would chant or do a calling around the site to harness the energy. You might think of it as an American Indian rain dance. We can still do that and sometimes we don’t now we are even doing it.

Here's an example from Tamar George. “One day I was driving over the Fort Pitt Bridge and there was only one cloud in the sky and it was dropping raindrops only in the Three Rivers Stadium. I knew my son was there at the stadium for a rock and roll concert. The announcer on my car radio said, “This is the strangest thing, folks. I’m looking out my window from the Gateway building and the sky and it is raining on the stadium.” When I returned home, I asked my son if he had been praying for rain. He replied that everyone was praying for rain because it was so incredibly hot in the stadium.”

Pittsburgh has long been recognized as a power place.