This is the best thing you can buy when you get to Lisbon! For €33,50, you get 2 cards, one for transports and one for discounts. The transports is a free pass on all tram, bus, metro and train lines. The discounts gives free or discounted access to most museums and exhibitions, and also discounts in some shops. You also get a map and a guide. A complete kit to get to know Lisbon very well!
I lived in Lisbon for 20 years and got the Lisboa Card, and was pleasantly surprised!