An old bridge, rusted and overgrown with weeds. A dark, cramped basement. A lonely country road. These are a few of the sites that photographer Amani Willett has brilliantly captured in his “Underground Railroad: Hiding in Place” photo series. Willett, who is gearing up to publish a historical book project this fall, decided to document forgotten locations across America that once served as stops on the famous, secret network of trails and hiding places that led runaway slaves to freedom.

A Brooklyn-based photographer whose work has been featured in Newsweek and The New York Times, Willett has been taking photos for nearly 20 years. His work has always centered on questions of history, memory, family and narrative. In “The Underground Railroad” series, he investigates how history and memory play a role in the energy of a place.

After extensive research, the photographer mapped out locations he felt had potential to be photographed ― and they didn’t have to be famous landmarks.

“I’m mainly interested in places that have not been well-marked or otherwise memorialized,” Willet told The Huffington Post. “It fascinates me that these sites carry an invisible history that, through photography, can be revealed.”

Willett took photographs over several years beginning in 2010 in locations including Queens, New York and Christiana, Pennsylvania, but he says his most personal and profound experience was visiting an Underground Railroad site in Cambridge, Massachusetts, not far from where he grew up.

“I would spend time in the same location as a kid totally unaware of its greater context in American history,” Willett says.

“Once I learned what took place there hundreds of years ago, the site’s meaning completely transformed for me. Every time I’m visiting my parents I pass by and just stop to take it all in for a moment.”

Check out photos from “The Underground Railroad: Hiding in Place” series with captions by Amani Willett below:

"Night Crossing," Columbia, Pa. Amani Willett The water in this location of the Susquehanna River is shallow and enabled many attempts for crossing the river at night. And because of the county's location near the Mason-Dixie line, it was a route heavily travelled by freedom-seekers.

"Wayside," Concord, Mass. Amani Willett A fugitive slave was sheltered overnight in these woods in early 1847. The woods are on the property of the Wayside Inn, owned by the Alcott family.

"Red Bridges" Greensboro, Md. Amani Willett While freedom seekers traveling north were tempted to use bridges, they usually avoided them, as the threat of recapture was high. This stream at the headwaters of the Choptank River was on Harriet Tubman's Underground Railroad route to Sandtown, Delaware.

"Bowen's Basement," Cambridge, Mass. Amani Willett The basement of Joshua Bowen Smith. Smith was an ardent abolitionist and state senator who, throughout his life, fought vigorously for the abolitionist cause. Along with Lewis Hayden, he publicly denounced the 1850 Fugitive Slave Act, which made it a federal crime to assist runaway slaves or impede the process of their re-apprehension. Furthermore he aided fugitive slaves by employing them as caterers in his business. It is rumored that he hid slaves in the basement of his house.

"Red Heart," Brooklyn, N.Y. Amani Willett This is one of the oldest Dutch Colonial farmhouses in Kings County and one of the largest slave holding estates in New York. There is speculation that slaves were hidden here on their way to Canada.

"Columbia Bridge," Columbia, Pa. Amani Willett A view of site of the original Columbia Bridge, which served as a landmark for fugitive slaves looking to cross the river. So important was Columbia in the slave-sheltering business that some think the term, Underground Railroad, was coined here.

"Beecher's Hand," Brooklyn, N.Y. Amani Willett A shadow cast from a sculpture of Henry Ward Beecher. The sculpture sits near his church in Brooklyn. Beecher was an American social reformer and speaker, known for his support of the abolition of slavery. In 1847, Beecher became the first pastor of the Plymouth Church in Brooklyn. Reflecting Beecher's views, the church was a station on the Underground Railroad.

"Christiana," Christiana, Pa. Amani Willett The 1850 federal Fugitive Slave Act strengthened the position of slave-owners seeking to capture runaways. Pursuing four escaped slaves, Maryland farmer Edward Gorsuch arrived on Sept. 11, 1851, at the Christiana home of William Parker, an African American who was giving them refuge. Neighbors and local residents defended fugitive slaves with firearms, killing Gorsuch, the slave-owner. Southerners demanded the hanging of those responsible. But after the first defendant was acquitted, the government dropped the case. The trial was the first nationally covered challenge to the Fugitive Slave Law of 1850 and did much to polarize the national debate over the slavery issue.

"Tunnel," Brooklyn, N.Y. Amani Willett Church of the Pilgrims, often called the "Grand Depot" because of the number of slaves that came through this location. Hundreds of escaped slaves were hidden in this basement.

"Bestpitch," Dorchester County, Md. Amani Willett Around this bridge, knowledgeable local escapees hid for days, even weeks, and followed the waterways north toward Caroline County and freedom. The location of the bridge provided good opportunities for escaped slaves to hunt, fish and gather food for survival. The area was also home to many free and enslaved African-American watermen. This provided opportunities for freedom-seekers to hitch an occasional ride or stow away in the holds of ships and sail away to freedom.

"Dismal Swamp," N.C. Amani Willett The Great Dismal Swamp made it an ideal place for those that didn't want to be found. For centuries, slaves came to the Dismal Swamp seeking freedom. For many, the sprawl of densely forested wetlands on the Virginia-North Carolina border was a stopping point on their journey northward. For others, the swamp became a permanent home where they established hidden, largely self-sufficient settlements called "Maroon" communities. Maroon communities developed throughout the American South, especially in inaccessible swampy areas. Recent research suggests that as many as 50,000 maroons may have lived in the swamp.

"Vicker's Tavern," Exton, Pa. Amani Willett In 1823, John Vickers, a skilled potter, fierce abolitionist and one of the most influential voices in the Lionville area, purchased the farmhouse that is now known as Vickers , now an award-winning restaurant in Chester County. For many years the Vickers farmhouse was known as the great central station in this part of Chester County. Slaves we hidden in the basement -- behind the door pictured -- of the house, which was also used as a pottery store.

"Duffield Street," Brooklyn, N.Y. Amani Willett One of two buildings on Duffield Street that were reportedly stops on the Underground Railroad. Residents claim there is a tunnel connecting the basements of the houses on Duffield Street. While the authenticity of this claim is still unproven, the current owners were able to successfully sue and stop a developer who was to have the house demolished.

"Hiding Place," Cambridge, Mass. Amani Willett It is rumored that a fugitive slave hid for the night in this park -- and eluded slave catchers -- while making the trip from Lewis Hayden's house in Boston to Joshua Bowen Smith's house in Cambridge.

"Side Door" Queens, N.Y. Amani Willett Site of a former church which was rumored to house fugitive slaves (usually overnight) until they left through a side door in the morning.

"Willett Church," New York, N.Y. Amani Willett In the corner of the church balcony near the end of a pew, there is a door (pictured) which leads to a narrow shaft to the attic. It has been frequently said that fugitive slaves were hidden there.

"Hoptank Landing," Preston, Md. Amani Willett Dr. Anthony C. Thompson owned 2,200 acres of heavily forested land near here during the late 1840s and 1850s. His timbering operations and sawmill employed large numbers of free and enslaved black laborers, including Harriet Tubman's father, Ben Ross. Harriet's parents were active in the Underground Railroad, and she most likely made her first escape close to this location. Later, on Christmas Day 1854, Harriet led her three brothers to freedom from here. Fearing her parents' exposure as agents, Harriet returned here to rescue them at great risk to herself.

"December 8th, 1855," Caroline County, Md. Amani Willett On December 8, 1855, Joseph Cornish started out on foot for Gilpin's Point, where he had heard there was a vessel about to sail. He hid in these woods until morning and was able to catch the boat. Once in Baltimore, Joseph made his way to Underground Railroad agent William Still in Philadelphia on Christmas Day. From there, Cornish was quickly forwarded to agent Sydney H. Gay in New York City. Cornish eventually made his way to St. Catharines, Ontario, Canada, where Harriet Tubman, her brothers and many others from Maryland's Eastern Shore were settling into their newfound freedom.

"Mason/Dixie," Maryland/Pennsylvania Border Amani Willett After Pennsylvania abolished slavery, the markers served as a demarcation line for the legality of slavery. Once fugitive slaves crossed north of the line, they were no longer considered legally enslaved.

"Grand Depot," Brooklyn, N.Y. Amani Willett This is Church of the Pilgrims, often called the “Grand Depot” because of the number of slaves that came through this location. Hundreds of escaped slaves were hidden in this basement over many years.

CORRECTION: This article previously misidentified The Wayside as The Wayside Inn, which is a different Massachusetts landmark.