Cork is the second city in the Republic of Ireland, with a population of approximately 123,000 people. Cork is also the principal city and administrative center of County Cork, and the largest city of the Province of Muster. The Lee River flows through the city, forming an island which is the main part of the city. Cork Harbor is one of the world's largest harbors. Cork is a major seaport, with docks all over Lee's east side. Notable attractions include two cathedrals and an opera house. Cork has some very fine architecture, comparable to Dublin or Belfast. Patrick Street is the main thoroughfare, and was remodeled in 2004. It gets a lot of pedestrian traffic because it is the main shopping street. Grand Parade, another section of the street, is a tree-lined avenue home to offices and financial institutions. Other buildings of different eras, as well as new modern buildings, and County Hall Tower is the tallest building in the Republic of Ireland. Across the river is Ireland's longest building, the Mental Hospital built in Victorian times. The seaport, Cobh, is in County Cork.