This city has an elaborate network of transit and transportation systems. There are electric trams that are 50+ years old, there are modern trams that are new this year, traditional buses, Metro lines, trains and taxis. Getting to and fro about town is fairly simple if you know the routes of the network.
Being a visitor I know a little about what goes where. I do have a good understanding of the Metro and train systems. Buses are challenging, some of the routes don't make sense to a new comer. Each bus has a route number and displays the end point of the route. This requires you understand the location of the end point.
Sometimes I roll the dice, spin the chamber on the transit gun and just get on board the next unfamilar bus. Where it goes unfolds like a travel log of Lisbon's barrios and back streets. I may waste 30 minutes going somewhere I had not intended to go, but I don't see it as wasted time, I am an explorer playing Lisbon roulette.