The UW–Madison campus has four buildings that have earned National Historic Landmark status — meaning that the federal government has cited them as among the 2,500 places in the country with the most historical significance. These include the Armory and Gymnasium (the Red Gym), North Hall, Science Hall, and the Dairy Barn. They aren’t necessarily the oldest buildings on campus, nor are they, by any means, the most important. But each has made its own unique contribution to the UW and to architecture.

1. North Hall is the UW’s oldest building, opened in 1851. It’s housed dorm rooms, classrooms, lecture halls, and labs. It was also the first campus building to be named a landmark, acquiring that honor in 1965. Today it’s home to the Department of Political Science.
2. The Red Gym looks like a castle in part because it was originally meant to serve a military purpose: the state government feared labor riots in the 1890s, when the structure was built, so the building was designed to store armaments for the national guard. It also housed ROTC offices until the 1970s.
3. Science Hall is the second building to bear that name on the UW campus, but after the first burned, university administrators determined that the current edition would be completely fireproof. It was the most expensive state building of its time, and it was one of the first buildings in the United States with a skeleton of structural steel. Essentially, it paved the way for later skyscrapers. Legend holds that undergraduate Frank Lloyd Wright x1890 helped to design details for its windows. Both Science Hall and the Red Gym became National Historic Landmarks in 1993.
4. The Dairy Barn, built in 1898, includes a scientific innovation that, today, is taken completely for granted: a round silo. Designed by UW professor F. H. King, the round silo helped farmers to solve the problem of how to keep animal feed from rotting before they could feed it to their animals. The Dairy Barn’s silo is one of the first that America ever saw. Named a landmark in 2005, it’s the UW’s most recent inductee to that honor.

Campus has a great many historic buildings (I would have put Gordon Commons on the list as the place where Juston Stix were created, but nobody asked me), but only these four have received the U.S. government’s highest historical-architecture honor.