The Lisboa Card allows you unlimited use of Lisbon’s public transport, and also gives you free entry to 26 museums and places of interest. It also gives small discounts for the other attractions not included.
In addition to transport inside Lisbon, you can travel free using the card on the Sete-Rios-Sintra-Oriente and Cais do Sodré-Cascais trains.
The card is worth it for those travellers that want to visit places such as Sintra or Cascais, as the train is included in the price. To see if it’s worth it for the other travellers, you’ll have to research a little more.
For students and young-persons travel card holders, the Lisboa Card isn't worth it under any circumstances. These two groups can get big discounts for the attractions.
The Lisboa Card can be purchased for periods of 24, 48 or 72 hours.
The most convenient (and in certain periods, the cheapest) thing to do is buy the card before arriving in Lisbon. You can purchase it online by following this link:
You can also get discounts on the rest of the attractions that range from 10% to 50%.