Tram 28 is a pickpocket express and locals avoid it like the plague. That hostel owner gave you good advice. Lisbon is built on seven hills and the whole city is a maze of tiny streets you can't see from a tram window. Walking is the only way you'll accidentally find the good bakeries and viewpoints. I spent four days there on foot and my legs were dead but I saw way more than the people packed in that yellow box.