The oldest opera house in the United States still used for its original purpose

First off, let's clear up the naming logistics. Despite the name, the Academy of Music has never actually contained a music school. It's a classic case of branding over function. It is, however, the oldest opera house in the United States still used for its original purpose. They call it the Grand Old Lady of Locust Street.

Construction started in 1855 after the architects won a design competition. They used a Rundbogenstil style from Germany, featuring those signature round arches. To save some serious cash for the interior, they went with a plain brick and brownstone exterior. A smart move. It allowed them to spend the budget on an open horseshoe auditorium and a three-foot brick wall lined with pine boards to keep the acoustics from turning into a chaotic echo chamber.

The grand ball hit the floor in January 1857. A month later, the Max Maretzek Italian Opera Company took the stage for the first production of Verdi's Il trovatore. It was the Western Hemisphere premiere. The New York Times described the theater as magnificently gorgeous, brilliantly lighted, solidly constructed, finely located, and beautifully ornamented.

Today, it still functions as a primary venue for the Philadelphia Ballet and Opera Philadelphia. It holds about 2,389 seats, though records from 1947 reported a capacity of 3,052. It has survived indoor football games, political conventions, and a century of orchestral residency. It still stands, still performs, and still refuses to admit it is not a school.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons