Dubai  is the largest and most populous cityin the United Arab Emirates (UAE). On the southeast coast of the Persian Gulf, it is the capital of the Emirate of Dubai, one of the seven emirates that make up the country.

Dubai is a global city and business hub of the Middle East. It is also a major global transport hub for passengers and cargo. Oil revenue helped accelerate the development of the city, which was already a major mercantile hub, but Dubai's oil reserves are limited and production levels are low: today, less than 5% of the emirate's revenue comes from oil. A growing centre for regional and international trade since the early 20th century, Dubai's economy today relies on revenues from trade, tourism, aviation, real estate, and financial services.

Dubai has attracted world attention through large construction projects and sports events, in particular the world's tallest building, the Burj Khalifa. As of 2012, Dubai was the most expensive city in the Middle East. In 2014, Dubai's hotel rooms were rated as the second most expensive in the world.

Dubai  is the largest and most populous cityin the United Arab Emirates (UAE). On the southeast coast of the Persian Gulf, it is the capital of the Emirate of Dubai, one of the seven emirates that make up the country.

Dubai is a global city and business hub of the Middle East. It is also a major global transport hub for passengers and cargo. Oil revenue helped accelerate the development of the city, which was already a major mercantile hub, but Dubai's oil reserves are limited and production levels are low: today, less than 5% of the emirate's revenue comes from oil. A growing centre for regional and international trade since the early 20th century, Dubai's economy today relies on revenues from trade, tourism, aviation, real estate, and financial services.

Dubai has attracted world attention through large construction projects and sports events, in particular the world's tallest building, the Burj Khalifa. As of 2012, Dubai was the most expensive city in the Middle East. In 2014, Dubai's hotel rooms were rated as the second most expensive in the world.

Muscat is the capital and largest city of Oman. It is the seat of the Governorate of Muscat. According to the National Centre for Statistics and Information (NCSI), the total population of Muscat Governorate reached 1.4 million as of September 2018. The metropolitan area spans approximately 3,500 km2 (1,400 sq mi) and includes six provinces called wilayats. Known since the early 1st century CE as an important trading port between the west and the east, Muscat was ruled by various indigenous tribes as well as foreign powers such as the Persians, the Portuguese Empire, the Iberian Union and the Ottoman Empire at various points in its history. A regional military power in the 18th century, Muscat's influence extended as far as East Africa and Zanzibar. As an important port-town in the Gulf of Oman, Muscat attracted foreign tradesmen and settlers such as the Persians and the Balochis. Since the ascension of Qaboos bin Said as Sultan of Oman in 1970, Muscat has experienced rapid infrastructural development that has led to the growth of a vibrant economy and a multi-ethnic society.

Santorini, classically Thera, and officially Thira, is an island in the southern Aegean Sea, about 200 km (120 mi) southeast of Greece's mainland. It is the largest island of a small, circular archipelago, which bears the same name and is the remnant of a volcanic caldera. It forms the southernmost member of the Cyclades group of islands, with an area of approximately 73 km2 (28 sq mi) and a 2011 census population of 15,550. The municipality of Santorini includes the inhabited islands of Santorini and Therasia and the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, and Christiana. The total land area is 90.623 km2 (34.990 sq mi).Santorini is part of the Thira regional unit.

The island was the site of one of the largest volcanic eruptions in recorded history: the Minoan eruption(sometimes called the Thera eruption), which occurred about 3,600 years ago at the height of the Minoan civilization. The eruption left a large caldera surrounded by volcanic ash deposits hundreds of metres deep. It may have led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km (68 mi) to the south, through a gigantic tsunami. Another popular theory holds that the Thera eruption is the source of the legend of Atlantis.

It is the most active volcanic centre in the South Aegean Volcanic Arc, though what remains today is chiefly a water-filled caldera. The volcanic arc is approximately 500 km (310 mi) long and 20 to 40 km (12 to 25 mi) wide. The region first became volcanically active around 3–4 million years ago[citation needed], though volcanism on Thera began around 2 million years ago with the extrusion of dacitic lavas from vents around the Akrotiri.

 Barcelona is a city in Spain. It is the capital and largest city of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within city limits, its urban area extends to numerous neighbouring municipalities within the Province of Barcelona and is home to around 4.8 million people, making it the sixth most populous urban area in the European Union after Paris, London, Madrid, the Ruhr area and Milan. It is one of the largest metropolises on the Mediterranean Sea, located on the coast between the mouths of the rivers Llobregat and Besòs, and bounded to the west by the Serra de Collserola mountain range, the tallest peak of which is 512 metres (1,680 feet) high.

Founded as a Roman city, in the Middle Ages Barcelona became the capital of the County of Barcelona. After merging with the Kingdom of Aragon, Barcelona continued to be an important city in the Crown of Aragon as an economic and administrative centre of this Crown and the capital of the Principality of Catalonia. Barcelona has a rich cultural heritage and is today an important cultural centre and a major tourist destination. Particularly renowned are the architectural works of Antoni Gaudí and Lluís Domènech i Montaner, which have been designated UNESCO World Heritage Sites. The headquarters of the Union for the Mediterranean are located in Barcelona. The city is known for hosting the 1992 Summer Olympics as well as world-class conferences and expositions and also many international sport tournaments.

Barcelona is one of the world's leading tourist, economic, trade fair and cultural centres, and its influence in commerce, education, entertainment, media, fashion, science, and the arts all contribute to its status as one of the world's major global cities. It is a major cultural and economic centre in southwestern Europe, 24th in the world (before Zürich, after Frankfurt) and a financial centre. In 2008 it was the fourth most economically powerful city by GDP in the European Union and 35th in the world with GDP amounting to €177 billion. In 2012 Barcelona had a GDP of $170 billion; and it was leading Spain in employment rate in that moment.

In 2009 the city was ranked Europe's third and one of the world's most successful as a city brand. In the same year the city was ranked Europe's fourth best city for business and fastest improving European city, with growth improved by 17% per year, and the city has been experiencing strong and renewed growth for the past three years. Since 2011 Barcelona has been a leading smart city in Europe. Barcelona is a transport hub, with the Port of Barcelona being one of Europe's principal seaports and busiest European passenger port, an international airport, Barcelona–El Prat Airport, which handles over 50 million passengers per year, an extensive motorway network, and a high-speed rail line with a link to France and the rest of Europe.