The Old Lisbon bus tour was incredible, great for seeing the city and saving your legs as their are heaps of steep inclines.
The Modern Lisbon bus tour, was also interesting. At the beginning you start by working your way around the rights streets, very exciting. Then you make stops at the Tile Musuem, which was a highlight, and the Oceanarium, a great place to visit in the heat of the day. The rest of the tour was interesting for modern architecture.
Overall an amazing experience!
Note that on Mondays that most if not all, Museum's and historic sights are closed. So if you are staying for more than a couple of days, time your booking.