What is a must to see when visiting Lisbon in Portugal?

and also some other 'hidden' treasures for visitors

Besides what all books say (Bel茅m area, Chiado, Downtown, Alfama, Bairro Alto and so on), some tips:

- Just walk away throughout the streets. It麓s the best way to discover the beauty and the essence of Lisbon.
- Catch one of the old trams, for instance the E28. It麓s a lovely way to feel the city.
- Go to a Fado house.
- Eat in those restaurants that looks traditional. Most of the times they seems old, but they serve good food. Try Cod fish (Bacalhau) and Cozido 脿 Portuguesa.
- Eat a "febra" with Sumol of pineapple or orange. You will love!

and so on so on so on...

The Vasco da Gama Bridge
Cristo Rei of Lisboa
Parque das Na莽玫es (Park of the Nations)

IN LISABON

Pra莽a do Com茅rcio
Monument to the Discoveries
Castelo de S茫o Jorge
Torre de Bel茅m
Elevador da Gl贸ria
Planetarium
Elevador de Santa Justa
Tarts of Bel茅m
Igreja do Carmo
Ponte 25 de Abril
Eduardo VII Park
Ponte Vasco da Gama
Pra莽a Marqu锚s de Pombal
Botanical Gardens
Avenida da Liberdade
Jardim Zool贸gico
Pra莽a dos Restauradores
Pal谩cio de S茫o Bento
Pra莽a da Figueira
Pal谩cio de Queluz
Rua Augusta
Pal谩cio de Mafra
Rossio Pal谩cio da Pena
Rossio Station
Praia do Guincho
Chiado
Costa da Caparica
Miradouro de S茫o Pedro
Arr谩bida Mountains
Expo Park
Alfama
Cascais
Pal谩cio de Bel茅m
Sintra
Mosteiro dos Jer贸nimos
Museums

Fado restaurant.
you need to go to a fado night and enjoy the Portuguese culture.

The Benfica Stadium! (Est谩dio da Luz)

From all the answers here, Luis gave the best answer!!!

Catch the trams and you will see the old/real Lisbon.
Catch also the Elevador da Gloria (tram) and enjoy the view.

Visit the Se cathedral.And Mosteiro dos Jeronimos.
Visit also Convento de Mafra which is outside of Lisbon and Palacio da Pena in Sintra.

Visit Chiado and Bairro Alto.A Must!!!

And also Cristo Rei on the other side of river.

Enjoy Lisbon :)