Twelve thousand years ago, this area lay at the bottom of Glacial Lake Wisconsin, an 1825 square mile lake formed when glacial ice blocked the Wisconsin River and backed water up to Stevens Point. The valley here was a long narrow bay of the lake, with surrounding sandstone bluffs forming the shoreline, and the flat lake bed later provided an ideal route for a railway that became the 400 Trail. The large sandstone outcrop beyond this point, known locally as the Third Castle, stood as an island in Glacial Lake Wisconsin. Its name, like those of the First and Second Castles to the left, came from European settlers who thought these rock bluffs resembled the walls of castles from their homelands. The area north of Third Castle remains shaded most of the day, creating a cool climate where hemlock trees, usually found farther north, can grow in the cliff’s shade.