Confusion Hill, Optical illusion amusement park in Piercy, California, United States.

Confusion Hill is a roadside attraction in Piercy, California, opened in 1949. Its Gravity House is a wooden building with a sharply slanted, sagging shingle roof, a black entryway, a yellow-framed window with a cross-shaped divider, and a yellow awning edge. A wooden picket fence encloses a small sloping area beside it, and a yellow sign on a tree reads "CONFU" with a red arrow pointing left.

Confusion Hill opened in 1949 beside US 101, the Redwood Highway, and for sixty years drew travelers passing through Piercy. Repeated mudslides led to the highway's realignment in 2009 onto the Confusion Hill Bridges, which bypassed the attraction. In 2010 it was granted California Points of Historical Interest status.

The yellow sign on the tree trunk reading "CONFU" with a red arrow points visitors toward the entrance. Since 2016 the grounds have held a statue of Bill Cipher, the antagonist of the animated series Gravity Falls, installed by its creator Alex Hirsch after a global scavenger hunt called the Cipher Hunt.

The site sits about 25 miles (40 kilometers) south of Avenue of the Giants and offers a miniature train ride, gift shop, and playground. The facility suits families with children and allows for roughly an hour-long visit.

The Gravity House is one of several such tilt buildings in the United States, but its setting is unusual: it stood directly on US 101, the Redwood Highway, for 60 years. When mudslides forced the highway onto the Confusion Hill Bridges in 2009, the attraction was left beside the old road. In August 2016 Alex Hirsch placed a statue of Gravity Falls villain Bill Cipher here after a global scavenger hunt.