London's location is the United Kingdom.
The British Library is the national library of the United Kingdom and the second largest library in the world by number of items catalogued . London . The London Underground is the oldest underground railway network in the world . The London Underground ( also known simply as the Underground , or by its nickname the Tube ) is a public rapid transit system serving London and some parts of the adjacent counties of Buckinghamshire , Essex and Hertfordshire in the United Kingdom .