Complex sentence: University Hall was actually the second building constructed on the Northwestern University campus; the building known as "Old College" was constructed as a temporary building in 1855, though it stood on campus until the 1970s.
Split into simpler sentences: University Hall was actually the second building constructed on the Northwestern University campus. The building known as "Old College" was constructed as a temporary building in 1855, though it stood on campus until the 1970s.