CC BY-NC-ND “Associação de Turismo do Porto e Norte, AR”
Located along the Douro river estuary in northern Portugal, Porto is one of the oldest European centers, and registered as a World Heritage Site by UNESCO in 1996. 
Its Latin name, Portus Cale, has been referred to as the origin for the name "Portugal", based on transliteration and oral evolution from Latin. In Portuguese the name of the city is spelled with a definite article as "o Porto" (English: the port). 
Consequently, its English name evolved from a misinterpretation of the oral pronunciation and referred to as "Oporto" in modern literature and by many speakers. 
In recent years, UNESCO recognized its historic center as a World Heritage Site. 
For more information, please see Turismo de Portugal web site (also includes information about cultural events, places to visit, etc.).