Centennial Tunnel is located in Poblacion, Aringay, La Union, Philippines.

The 500 meter tunnel was made in 1913 during the American regime. Intended for the trains of the Philippine National Railways (PNR) bound for Baguio City, it was later abandoned by the Commonwealth Govenment because of the then impending Second World War. According to locals, the tunnel already exists during the Spanish era, it was only in the American occupation that it was developed and fortified, thus making it officially more than a century year old. During the Japanese occupation, the tunnel was used as headquarters of the Japanese Imperial Army because of its durability against US bombings, rising speculations that hidden treasures were buried in the area.

Source:

Launion.gov.ph