Lots of hills in Lisbon but very walkable but absolutely in sneakers or something with a tread....Watch the 'Somebody Feed Phil' Lisbon episode on Netflix and Eugene Levy's "Reluctant Traveler' Lisbon episode on Apple TV...and get ready to fall in love with the city!
Dining
MiniBar (Dinner), Jesus e Goes (Jesus from Goa) for lunch, O Faia (for dinner and Fado show), TimeOut Lisbon (for lunch), Manteigaria for pasteis de nata (get ready to eat alot of them...and lots of options for this delicious pastry....) if you make it to Belem (and why wouldn't you? short tram ride) go to Pasteis de Belem for coffee and and the pastry....There are endless options for great food in Lisbon
Shopping - A Vida Portuguesa for Portuguese home goods...great store
Sightseeing
Just walking around the city is spectacular...its gorgeous. Its the oldest European capital so do not expect it to be as pristine as say Disney World. English is spoken quite frequently and the people are very hospitable and friendly.
Núcleo Arqueológico da Rua dos Correeiros (Fundação Millennium bcp) - archeological dig dating back to the bronze age. You get to walk down through the centuries, it is very well done and free!
Castelo de S. Jorge - book your tix online and stroll right in...afterwards walk through the Alfama neighborhood (Rick has a great walk in his Lisbon book)
every Miradouro (city viewpoints) you can get to...
Jeronimos Monastery ,Belem Tower, Monument of the Discoveries in Belem were highlights for us.
Have fun!