When a local shows you around, you learn to see things differently. When that local has survived one of the most notorious massacres in the history of his country, it's more than a little bit different.

We were guided through the plazas and apartment blocks of Bloody Sunday in Derry, Northern Ireland by Jon McCourt, who has lived his whole life in Derry, much of it within sight of the massacre. It's Derry to the Catholics and Nationalists, like McCourt; the Unionists call it Londonderry.

We started our tour in the city centre, where we climbed to the top of the city walls—built by Ulster Protestants between 1613 and 1618. This city has maintained its original wall, which has never been breached by an invader—thus its nickname (one among many), "The Maiden City."

Still in the 17th Century, Catholic King James II of England (also on the throne of Scotland and Ireland) came to the city and was refused admission when a group of 13 "apprentice boys"—young men training in the various trades—got hold of the keys to all the city gates and locked the king and his men outside. The king, in turn, besieged the city for 105 days, blockading the river so supply ships couldn't deliver food and arms.

But when someone hung a crimson banner (rumored to have been dyed red by the blood of martyrs defending the walls), the ship captains knew the tides were right to run the blockade. And once the blockade was broken, James, knowing he had been unable to defeat Londonderry when it was starving, knew he could never take the city when its men had been fed.

The walls go alongside the Fountain, the only Protestant community still on the city centre side of the Foyle River. Jon pointed out the gates facing the very Nationalist neighborhoods of Bogside and Craggin, which are locked each evening at 8 p.m. to keep Catholics and Protestants out of each other's hair. Gates atop the city walls are also locked during times of expected trouble, so Nationalists could not throw rocks or petrol bombs at the Protestant homes. He noted that even though there are many shops and services immediately outside the area, most locals are afraid to use them, and cross to the Waterside, the Unionist side of the river. A just-completed playground is the first service within the Fountain.

Each major church had its own primary school, but as Protestants left the city side of the Foyle for Waterside, many of the denominations could no longer support a school of their own. The one remaining Protestant grammar school on the Nationalist side of the river is now mixed-denomination, and many of its students are bussed in.

While the city and its neighborhoods are now committed to peace, and Loyalists work with Nationalists in all sorts of reconciliation activities, the tension hasn't gone away entirely. Signs and memorials and political graffiti are constantly visible. In Fountain, you'll see a large marker announcing that Londonderry Loyalists are "still under siege." In Bogside, a mural states that co-operation with the police is betrayal. On the Bogside face of the city wall, slogans demand the release of certain prisoners.

Still, there's a general understanding that 30 years of violence did not help anyone's cause, and the need to move on is beautifully expressed in the recently opened Peace Bridge, a pedestrian crossing between the city centre and Waterside, where the vast majority of Loyalists live. We were told that people who had never been to the opposite neighborhood crossed the bridge the day it was opened, and it's much used by both tourists and locals.

The walled city used to be an island. Most of downtown outside the city walls is on reclaimed land formerly under the River Foyle; the name Bogside was given as the lands started to dry out into bogs. Since Catholics were not allowed to reside within the walls, they settled here. Looking out onto Bogside, Jon pointed out Free Derry Corner

Then we came down from the wall—and it got very personal. "Here's where they killed an 11-year old boy, shooting a rubber bullet into his head at 200 miles per hour. Over here is where my friend Michael Kelly tried to help, and was shot."

Every block and alley had its own tragedy, either on Bloody Sunday or on a different day, and Jon McCourt knew all of their names, ages, and how they died. He knew where each unit of four soldiers were deployed, and when and how they fired. He showed us pictures taken that day by a French news photographer, Gilles Peress—and one that he hadn't seen until many years later when he testified before the inquiry commission, showing him in the scene he describes:

"Over here is where James Wray and I were running to take cover. When I got to the corner, James was no longer beside me. I didn't realize at first that he had been killed. We used to play basketball together. And then I looked across and saw the soldier, holding his rifle in shooting position. He looked at me, shrugged, and pointed his rifle down.

"Five people in my grade school class of 1964 were killed in the Troubles; I watched three of them die." Seven of the 14 people massacred on Bloody Sunday were teenagers. More than 3000 people on both sides died in the violence over a 30-year period.

The tour ended at the Museum of Free Derry, in a converted row house at the site of the shootings. For a nominal admission charge, we got to see newspaper clippings of the massacre, artifacts ranging from the bloodstained banner carried by the marchers to a vinyl record of Irish freedom songs to racist hate mail some of the victim families received later. Jon showed us the rubber bullet that had been shot at his mother, and said it had been displayed on a windowsill in his house for 30 years, until his mother gave it to the museum on her 90th birthday. Periodically, the Royal Ulster Constabulary or the British army would search his house, and some would try to take the bullet. One man did steal it, and Jon's mother ran out to the armored car and beat him with her slipper until he gave it back. The caption outside the display case simply credits Anna McCourt. This is about 20 feet down the hall from a series of photographs showing James Wray with his grandparents outside their Bogside cottage, and then the grandparents showing the bullet holes in their house. The picture hangs in the spot were those bullets lodged into the walls, and the outside wall of the museum still shows bullet holes.

Yet even though it touched him so closely, Jon McCourt—a former IRA man, close-range witness to Bloody Sunday, and ardent Irish Nationalist—has spent the last three decades doing reconciliation work, partnering with former Loyalists to teach peace and conflict resolution in schools and in a program educating American university students.

The Museum of Free Derry offers walking tours of Free Derry and Bogside, covering the origins of the conflict, the Irish Civil Rights movement, and other key events. For one pound extra, you can also tour the museum. Jon McCourt is not one of the museum's guides, but the ones who lead these tours are also people who were personally affected. Email freederrytours@gmail.com, visitwww.freederry.net, or call 0779 3285 972.

Peace activist and writer Shel Horowitz took the Bloody Sunday tour as apart of a week-long peace and conflict resolution intensive at Inch House, in Donegal, Ireland, eight miles from Derry, organized annually by Isenberg School of Management, University of Massachusetts at Amherst.