Pittsburgh is the second largest city in the U.S. Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of both Appalachia and the Ohio River Valley.The characteristic shape of Pittsburgh's central business district is a triangular tract carved by the Confluence of the Allegheny and Monongahela rivers, which form the Ohio River.
The city features 151 high-rise buildings,446 bridges,two inclined railways, and a pre-revolutionary fortification. Pittsburgh is known colloquially as "the City of Bridges" and "the Steel City" for its many bridges and former steel manufacturing base.Pittsburgh still maintains its status as a corporate headquarters city, with eight Fortune 500 companies calling the city home.
Pittsburgh museums include the Andy Warhol Museum, the Carnegie Museum of Art, the Frick Art & Historical Center, Pittsburgh Center for the Arts and the Mattress Factory. Installation art is featured outdoors at ArtGardens of Pittsburgh. The Carnegie Museum Of Natural History has extensive dinosaur collections and an Ancient Egypt wing.The city is also served by the Pittsburgh Zoo and PPG Aquarium, Phipps Conservatory and Botanical Gardens, and the National Aviary.