The Exeter Secret Tunnels are a major mystery as they have never actually been found or discovered, they have only been rumored to exist. The story goes back a long time and the tunnels are said to be linked to the Underground Railroad. Robbins Paxton Gilman even tackles the legend on these tunnels in his narrative: The Old Logg House by the Bridge.
The secret underground tunnels have been rumored to be near Franklin & Clifford Street. Legend has it that the tunnels intersect in the basement of the Gilman Garrison house which was constructed in 1709. The US Department of Interior undertook a project to document and survey the house. Their research has never been publicly revealed!
The Underground Railroad was a network of secret routes and safe houses established in the United States during the early-to-mid 19th century, and used by African-American slaves to escape into free states and Canada with the aid of abolitionists and allies who were sympathetic to their cause. The term is also applied to the abolitionists, both black and white, free and enslaved, who aided the fugitives. Various other routes led to Mexico or overseas. An earlier escape route running south toward Florida, then a Spanish possession (except 1763–83), existed from the late 17th century until Florida became a United States territory in 1821 (and ending the safe haven for escaped slaves was the main reason it changed nationality). However, the network now generally known as the Underground Railroad was formed in the late 1700s, and reached its height between 1850 and 1860. One estimate suggests that by 1850, 100,000 slaves had escaped via the "Railroad".
British North America (present-day Canada), where slavery was prohibited, was a popular destination, as its long border gave many points of access. Most former slaves settled in Ontario. More than 30,000 people were said to have escaped there via the network during its 20-year peak period, although U.S. Census figures account for only 6,000. Numerous fugitives' stories are documented in the 1872 book The Underground Railroad Records by William Still, an abolitionist who then headed the Philadelphia Vigilance Committee.Provided By: https://en.wikipedia.org/wiki/Underground_Railroad