UK events, UK travel packages, United Kingdome tours, Places to visit in UK, Holidays in UK, Holiday packages in UK, Online booking travel packages. http://www.ukvisit.net/ The London Underground is an underground railway system - also known as a rapid transit system (Tube). London is served by 12 Tube lines. It is the world's oldest underground system. The Underground has 275 stations and runs over 253 miles (408 km) of line. http://www.ukvisit.net/london-underground.shtml http://www.ukvisit.net/london-underground.shtml