A New York City teacher, Bob Moses went to Mississippi and helped organize the largest grassroots civil rights campaign the country had ever seen. "Freedom Summer" premieres on American Experience PBS on June 24 at 9/8c.

"People in the movement were willing to die, but we didn't want to die in obscurity. So if we brought in students, their colleges, their parents would focus on Mississippi." "Freedom Summer" premieres on American Experience PBS on June 24.

Fannie Lou Hamer helped fight for better representation among Mississippi Democrats in 1964. Congressman Adam Clayton Powell of New York City asked for compromise. He didn't know who Fannie Lou Hamer was. Watch "Freedom Summer" on American Experience PBS on June 24, 2014.

In 1964, a group of civil rights organizations hosted The Mississippi Summer Project, a campaign that would later become known as "Freedom Summer." "It is very important to me that I play my role in civil rights for the U.S. and most of all for myself," wrote one volunteer. "Freedom Summer" premieres on American Experience PBS on June 24 at 9/8c.

Over 10 memorable weeks in 1964 known as Freedom Summer, more than 700 student volunteers from around the country joined organizers and local African Americans in a historic effort to shatter the foundations of white supremacy in Mississippi, then one of the nation’s most viciously racist, segregated states.

On August 6, 1964 the Mississippi Freedom Democratic Party held a statewide convention to elect 68 delegates to attend the Democratic National Convention later that month. It was Mississippi's first integrated delegation. Watch "Freedom Summer" on American Experience PBS on June 24, 2014.

In Freedom Schools across Mississippi, Freedom Summer workers and volunteers taught "African American History, Civics, African Culture, African Dance. They were learning black history that they were reading books that'd been written by blacks that they'd never heard of." "Freedom Summer" premieres on American Experience PBS June 24 at 9/8c.

Half a million people pass through New York City's Penn Station every day. During rush hour, a train arrives at a platform every 58 seconds. Phil Kaplan has worked for Amtrak for 37 years, and he takes us for an unusual behind the scenes look at the Central Control room.

Like engineering? Explore the Engineering Map of America and see how the most significant feats of science and technology across the US have transformed the landscape. Contribute your own photos and videos at pbs.org/engineeringmap, and download the Mapping History iPhone app!

The enormous engineering feat and one of the greatest architectural achievements of its time, Pennsylvania Station was torn down after just 53 years. Premieres on PBS American Experience February 18, 2014.

The Pennsylvania Railroad built tunnels under New York City's Hudson and East Rivers, connecting New York with New England, and terminating in one of the greatest architectural achievements of its time, Pennsylvania Station. It covered nearly eight acres, extended two city blocks, and housed one of the largest public spaces in the world. But 53 years later, the monumental building was destroyed.

As the Pennsylvania Railroad tunneled underneath the Hudson River, measurements showed that the tunnels were shifting up and down in the silty river bottom. Increasing the weight of cast iron linings did nothing to settle the tunnels, and the shifting continued. Engineers finally figured out what suddenly seemed obvious: the tunnels were moving with the tide.

Go underground in the MTA's East Side Access caverns and tunnels - just one of the projects in the MTA's portfolio of $18 billion of construction - which will connect Long Island Railroad trains directly to Manhattan's Grand Central Terminal.

In 1961, the financially strapped Pennsylvania Railroad announced it had sold the air rights above Penn Station. The company would tear down what had once been its crowning jewel to build Madison Square Garden, a high-rise office building and sports complex. Demolition began on October 28, 1963 and would continue for the next three years.

When the Pennsylvania Railroad announced they would be tunneling into Manhattan, rather than building a bridge, people were stunned. Tunneling underwater was known to be dangerous, and once they were built, the tunnels would need to withstand hundreds of trains traveling through them every day. With a typical Pennsylvania Railroad passenger train weighing 700 tons, this was no small challenge.

Excavation for the Pennsylvania Railroad's tunnel project was done by hand labor, with workers typically using a spade or pneumatic hammer. Excavation workers, called “sandhogs,” faced many dangers working in a confined space. Equipment was constantly moving in and out along with muck carts full of tons of mud and rock—and there was nowhere to run if things went awry.

Over 500 buildings were initially cleared for Penn Station’s construction, an area equal to two city blocks, or 28 acres. Crews worked day and night to build the train yard below ground, excavating tons of earth from the construction site. Avenues, buildings, and elevated railroads around the construction had to be propped up while workers excavated around the underground infrastructure.

Work never stopped on the Pennsylvania Railroad’s tunneling projects; there were three 8-hour shifts a day, 7 days a week. As the workers dug under the river bed, compressed air was pumped in to keep the water out of the tunnels. To bore under the river, the engineers used a Greathead shield, a steel cylinder with a diameter of 23 feet that weighed nearly 200 tons.

Masonry work began on Pennsylvania Station in 1908, and the grandeur of architect Charles McKim’s design began to take shape. Penn Station took four years to build and used 27,000 tons of steel, 500,000 cubic feet of granite, 83,000 square feet of skylights and 17 million bricks. Pennsylvania Station opened to the public in 1910.

The East River flowed over a mix of gravel, clay, sand, silt and bedrock. When sandhogs hit pockets of sand and gravel, there was a risk of air leaking from the tunnels. Workers were constantly on the alert for a whistling sound—a sign that compressed air was escaping and might at any moment punch a hole through the riverbed, known as a blowout. These blowouts were costly and often deadly.