The London Underground is famous because it provides a network to many areas in and around the city, including daily services to King's Cross/St. Pancras station and London Heathrow Airport, which is convenient to many passengers visiting different parts of the city.
Lisbon is famous in Portugal because it is capital city for example London is a famous city in England also Lisbon is the biggest city and tourists from other country's normally go stay there on there trip
The City of London and the city called London are two distinct places. The head of the City of London is the 'Lord Mayor of the City of London'. This should not be confused with the 'Mayor of London', who is in charge of the whole of Greater London.