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 enslaved African-Americans to escape into free states and Canada. The scheme was assisted by abolitionists and others sympathetic to the cause of the escapees. Not literally a railroad, the workers (both black and white, free and enslaved) who secretly aided the fugitives are also collectively referred to as the "Underground Railroad". Various other routes led to Mexico, where slavery had been abolished, 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. One of the main reasons Florida was purchased by the United States was to end its function as a safe haven for escaped slaves. However, the network now generally known as the Underground Railroad was formed in the late 1700s. It ran north and grew steadily until the Civil War began. One estimate suggests that by 1850, 100,000 slaves had escaped via the "Railroad".
British North America (present-day Canada) was a desirable destination, as its long border gave many points of access, it was further from slave catchers, and beyond the reach of the United States' Fugitive Slave Acts. Most former slaves, reaching Canada by boat across Lake Erie and Lake Ontario, 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