Poznań is a city on the Warta River in west-central Poland, in the Greater Poland region and is the fifth-largest city in Poland. It is best known for its renaissance Old Town and Ostrów Tumski Cathedral. Today, Poznań is an important cultural and business centre and one of Poland's most populous regions with many regional customs such as Saint John's Fair (Jarmark Świętojański), traditional Saint Martin's croissants and a local dialect.