TreeAlive maps family trees. When a visitor's ancestors lived in Pennsylvania, the markers standing near those places surface automatically alongside their family's journey:
Lancaster County Courthouse · under a mile from where their sixth-great-grandfather lived in 1756 · what this marker records spans 1739 to 1853, overlapping their sixth-great-grandfather's years here
When a marker stands near a place in your own tree, you have a personal reason to go see it. Open the live demo tree, choose the Crossings tab, and turn on Historical Markers to see it working.