People have lived on this rocky outcrop above the North Sea for at least three thousand years. Excavations at Oxwell Mains in 2003 uncovered the post-holes of a Mesolithic house from around the 9th millennium BC, a domed building from a time when Britain was still attached to continental Europe. A late Bronze Age skeleton, dated 800-540 BC, was found in the same general area. The Iron Age promontory fort whose perimeter is still preserved in the open ground of Castle Park was a principal centre of the Votadini, the British tribe the Romans noted on this coast. The name Dunbar comes from the Gaelic Dun Barra, summit fort, itself probably a Gaelicisation of an older Brittonic name with the same meaning. The fort, in some form, has been here since before recorded history.

Dunbar was absorbed into the Anglian kingdom of Northumbria in the 6th century. Bishop Wilfrid was imprisoned here in the 680s, the earliest written reference to the place. As Norse and Danish raids broke southern Northumbria's power, the northern portion was slowly absorbed into Scotland. Kenneth MacAlpin burned Dunbar in the 9th century. By the time Lothian was formally ceded to Malcolm II after the Battle of Carham in 1018, Dunbar had become Scottish. In 1072 Malcolm III granted the town and a wide swathe of East Lothian and Berwickshire to the exiled Northumbrian earl Gospatric, founding the House of Dunbar and the Earldom of Dunbar and March that would dominate this coast for nearly four centuries. Two major battles were fought near the town. The first, in 1296, opened the Wars of Scottish Independence. The second, in 1650, ended in a crushing defeat of the Scottish Covenanters by Oliver Cromwell, and led to the occupation of Scotland.

Muir was born on 21 April 1838, the third of eight children, in a tenement on the High Street. His father Daniel Muir was a religious zealot whose growing dissatisfaction with the Church of Scotland eventually drove the family across the Atlantic. The young Muir's Dunbar years were spent in the kind of unsupervised coastal childhood that would echo through everything he later wrote. He raced his brother through the cobbled wynds. He fished off the harbour. He explored caves below the castle and learned the names of seabirds nesting in the cliffs. Most importantly, he developed the habit of walking long distances and observing closely what he saw. After emigration, Muir worked his way through college in Wisconsin, walked a thousand miles from Indiana to Florida, was nearly blinded in an industrial accident in 1867, and afterwards committed himself to the natural world. His advocacy was central to the creation of Yosemite National Park in 1890 and the founding of the Sierra Club in 1892. The American National Park system has been called the best idea America ever had. The boy from Dunbar contributed more to that idea than any other person.

Long before Muir, the Dunbar landscape was defined by its castle. Built and rebuilt on a sea-rock above the harbour, it survived sieges that became Scottish legend. The most famous defender was Agnes Randolph, Countess of Dunbar, known as Black Agnes, who held the castle through a five-month English siege in 1338 while her husband was away. The stories say she walked the parapet in her best dress after each English bombardment, dusting the stone with a handkerchief to mock the besiegers. The castle was finally slighted by act of the Scottish Parliament in 1567, after Mary Queen of Scots had used it as a refuge in the disastrous weeks before her defeat at Carberry Hill. The Victorian engineers who built the new harbour in 1842 to 1844 quarried out the entire north end of the ruin for stone. What survives today is enough red sandstone to suggest the scale of one of the strongest medieval fortresses in Scotland.

Dunbar today is a working town of about 10,000 people. The harbour, dating from 1574, is still active, mostly landing shellfish. The Dunbar Lifeboat Station is the second-oldest RNLI station in Scotland. The town's two main manufacturers are Tarmac, running the only integrated cement plant in Scotland at Oxwell Mains, and Belhaven Brewery, producing Scottish Ale just outside town. Belhaven Bay, beyond the brewery, has become one of the best surfing beaches on the east coast of Scotland. Old Tom Morris laid out Dunbar Golf Club in 1894; it is used as a qualifying venue for the Open when the championship returns to Muirfield. The town's microclimate gives it more sunshine and less rain than almost anywhere else in Scotland, with about 1,450 hours of sun a year. On a summer evening on Belhaven Beach, with the Bass Rock and North Berwick Law in silhouette across the bay, it is easier to understand why a Scottish boy who emigrated to America would never quite stop missing this stretch of coast.