Derry

Colmcille's foundation of 546, rebuilt as a walled city in 1613 by the London livery companies who financed it — hence Londonderry, and hence the argument over the name that has never stopped. Its seventeenth-century walls have never been breached: thirteen apprentice boys shut the gates against King James in 1688 and the city held out for 105 days. 'No Surrender' entered the language here.

Derry is one of the oldest continuously inhabited places in Ireland. Its recorded history begins with the monastery Colmcille founded at Doire Calgach on the west bank of the Foyle, on land given by a local king; the traditional date of 546 is now thought to be a mistake by medieval chroniclers. For five centuries it was chiefly a monastery. In 1608 Sir Cahir O'Doherty burned much of the town and killed its governor.

In 1610 the Crown gave the town to the Irish Society of the London livery companies, who rebuilt it with walls as Londonderry. It was the first planned city in Ireland: begun in 1613, walls finished in 1619 at a cost of £10,757, four streets running from the central Diamond to four gates, a grid later copied across British North America. St Columb's Cathedral of 1633 is the oldest surviving building. In 1649 the Parliamentarian garrison was besieged by Scottish Presbyterian Royalists and relieved by an unlikely alliance of George Monck's troops and Owen Roe O'Neill.

Drawn from the History section of the Wikipedia article on Derry ↗, rewritten here and adding nothing it does not say; licensed CC BY-SA 4.0.

• Grianán of Aileach · fort · 8 km
• Burt Castle · castle · 13 km
• Altinaghree Castle · castle · 14 km
• Inch Castle · castle · 14 km
• Mongavlin Castle · castle · 14 km

Straight-line distances from the town centre, from each site's documented coordinates.

• Grianán of Aileach · The stone ring-fort of the Northern Uí Néill, 250 metres up above Lough Swilly, with terraces inside its walls for the assembled warriors of Ailech.
• Rathmullan · The pier from which the Earls sailed in September 1607 (Hugh O'Neill, Rory O'Donnell and ninety followers) never to return. Ulster's history pivots here.

All of these are pinned on the Hidden Ireland map.