What percentage of the London Underground is actually underground?
The London Underground is generally considered a marvel of public transport. The world's first underground railway train, a steam-operated engine, rumbled 3.5 miles through a tubular tunnel in 1863. The line was an instant success. More than 800 trains were operating by 1884. Today, millions of people reach their destinations each day through the London Underground. The tube network stretches for 249 miles, links together 270 stations, and uses more than 4100 trains to transport London's population. But the Underground title is a bit misleading. In reality, only about 45 percent of the railway's miles are underground. Source: MentalFloss.com