Maine is littered with old mill buildings that used to sustain towns and lives, and brought character and charm to some of the towns and cities they called home. As the mills began to close, some of the secrets that were kept within (or below) the walls of those buildings. One of the best kept secrets comes from Biddeford, where below the workings of an old mill lies the remnants of an a sprawling and spectacular underground lagoon.

According to Maine Today, the underground lagoon was a staple of the Pepperell #10 mill. A circuit of underground tunnels brought water from the Saco River to generate power for the old mills. Eventually, modern-day electricity took over, and the need to facilitate river water to the mills beneath the surface subsided, but the majestic subterranean rooms and tunnels still exist.

The Biddeford Mills Museum offers seasonal tours that will give people direct access to the stunning tunnels and of course, the underground lagoon. The tours typically last a couple hours, and you can revisit the history and significance of the mills in Biddeford's history.

Today, the Pepperell Mill is home to more than 100 businesses and and apartments. The repurposing of the Pepperell Mill has been one of the most successful in the state.