Downtown Pittsburgh is the main business district. It is constrained by two rivers, the Allegheny on the north and the Monongahela on the south. They join at what is known as the "Point", forming the Ohio river. Because it is thus limited it has been forced to grow upwards, and although Pittsburgh is in some ways a small town, its downtown contains some big town structures. Although there are numerous landmark buildings and notable structures in downtown, here are a few of the signature buildings of several large companies that make their headquarters in Pittsburgh.
The US Steel Building is a 64 story office building, the tallest structure between New York and Chicago. It is constructed of a special type of steel, "Corten" steel, developed by USS. It is not painted and is intended to rust to a tough, brown finish and then stop rusting. (One hopes.)
PPG Place is a unique set of buildings faced entirely with a glittering, sun inhibiting plate glass. It was developed by Pittsburgh Plate Glass as their headquarters. It sports ornate, yet modern, glass pinnacles like candles on a birthday cake.
Among these buildings is an unusual park which, in the winter, is flooded with water and used for ice skating, like Rockefeller Center in Manhattan.
The Alcoa Building is the first all aluminum building ever constructed. It stands 30 stories tall and is built of aluminum panels. Actually, Alcoa recently built a new building on the Northside and no longer occupies this landmark building which was built in 1953.
Point State Park is a delightful 36 acre park park located downtown where the tributary rivers join to form the Ohio. At its apex is a large fountain that forces a column of water 150 feet in the air. The base of the fountain is 200 feet in diameter. You can also see the Fort Pitt Museum and Blockhouse, the site where a famous battle was fought and from which control of the three rivers was maintained in colonial times, first by the French and later by the English.
The Cultural District is the name of an area where you may see symphony orchestra performances, opera, plays and many other events. The link offers a detailed map of this unique area in downtown Pittsburgh and provides a current schedule of events, nearby restaurants, parking, etc.