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.

Belfast is a port city in the United Kingdom and the capital city of Northern Ireland, on the banks of the River Lagan on the east coast of Ireland. It is the largest city in Northern Ireland and second largest on the island of Ireland. It had a population of 333,871 in 2015.

By the early 1800s Belfast was a major port. It played a key role in the Industrial Revolution, becoming the biggest linen producer in the world, earning it the nickname "Linenopolis". By the time it was granted city status in 1888, it was a major centre of Irish linen production, tobacco-processing and rope-making. Shipbuilding was also a key industry; the Harland and Wolff shipyard, where the RMS Titanic was built, was the world's biggest shipyard. It also has a major aerospace and missiles industry. Industrialisation and the inward migration it brought made Belfast Ireland's biggest city and it became the capital of Northern Ireland following the Partition of Ireland in 1922. Its status as a global industrial centre ended in the decades after the Second World War.

Belfast suffered greatly in the Troubles, and in the 1970s and 1980s was one of the world's most dangerous cities. However, the city is now considered to be one of the safest within the United Kingdom. Throughout the 21st century, the city has seen a sustained period of calm, free from the intense political violence of former years and has benefitted from substantial economic and commercial growth. Belfast remains a centre for industry, as well as the arts, higher education, business, and law, and is the economic engine of Northern Ireland. Belfast is still a major port, with commercial and industrial docks dominating the Belfast Lough shoreline, including the Harland and Wolff shipyard. It is served by two airports: George Best Belfast City Airport, and Belfast International Airport 15 miles (24 km) west of the city. It is listed by the Globalization and World Cities Research Network (GaWC) as a Gamma global city.

Oslo is the capital and most populous city of Norway. It constitutes both a county and a municipality. Founded in the year 1040 as Ánslo, and established as a trading place in 1048 by Harald Hardrada, the city was elevated to a bishopric in 1070 and a capital under Haakon V of Norway around 1300. Personal unions with Denmark from 1397 to 1523 and again from 1536 to 1814 reduced its influence, and with Sweden from 1814 to 1905 it functioned as a co-official capital. After being destroyed by a fire in 1624, during the reign of King Christian IV, a new city was built closer to Akershus Fortress and named Christiania in the king's honour. It was established as a municipality on 1 January 1838. The city's name was spelled Kristiania between 1877 and 1897 by state and municipal authorities. In 1925 the city was renamed Oslo.

the capital and chief port of Denmark, a city that occupies the eastern part of Zealand and northern part of the island of Amager; population 518,574 (2009).