Dublin is the capital of, and largest city in, Ireland. It is on the east coast of Ireland, in the province of Leinster, at the mouth of the River Liffey, and is bordered on the south by the Wicklow mountains. It has an urban area population of 1,173,179, while the population of the Dublin Region (formerly County Dublin), as of 2016, was 1,347,359, and the population of the Greater Dublin area was 1,904,806.

There is archaeological debate regarding precisely where Dublin was established by Celtic-speaking people in the 7th century AD. Later expanded as a Viking settlement, the Kingdom of Dublin, the city became Ireland's principal settlement following the Norman invasion. The city expanded rapidly from the 17th century and was briefly the second largest city in the British Empire before the Acts of Union in 1800. Following the partition of Ireland in 1922, Dublin became the capital of the Irish Free State, later renamed Ireland.

Dublin is a historical and contemporary centre for education, the arts, administration and industry. As of 2018 the city was listed by the Globalization and World Cities Research Network (GaWC) as a global city, with a ranking of "Alpha -", which places it amongst the top thirty cities in the world.

Reykjavík is the capital and largest city of Iceland. It is located in southwestern Iceland, on the southern shore of Faxa Bay. Its latitude is 64°08' N, making it the world's northernmost capital of a sovereign state. With a population of around 123,300 (and over 216,940 in the Capital Region), it is the heart of Iceland's cultural, economic and governmental activity, and is a popular tourist destination.

Reykjavík is believed to be the location of the first permanent settlement in Iceland, which, according to Ingólfr Arnarson, was established in AD 874. Until the 19th century, there was no urban development in the city location. The city was founded in 1786 as an official trading town and grew steadily over the following decades, as it transformed into a regional and later national centre of commerce, population, and governmental activities. It is among the cleanest, greenest, and safest cities in the world.