Sunol is an unincorporated area and census-designated place in Alameda County, California. Located in the Sunol Valley of the East Bay, the population was 913 at the 2010 census. It is best known as the location of the Sunol Water Temple and for its historic tourist railroad system, the Niles Canyon Railway.

Bedrock mortars used by Native Americans for pounding acorns that were found in the area are reminders of Sunol's first inhabitants. For the past century, however, the land known today as Sunol Regional Wilderness was used almost exclusively as ranch land.

The Niles Canyon Railway is a heritage railway that operates in Sunol, California, USA. The railway runs through scenic Niles Canyon, which is located between Sunol and the town of Niles in Fremont, California. The railway is operated by the Pacific Locomotive Association, a non-profit organization that is dedicated to the preservation of historic railway equipment.