As we decide what whether to stay in Lisbon or travel to it on day trips, one other factor seems relevant. Can one use public transportation, taxis, or whatever to address the Hills of Lisbon that I read about One person in our group of 4 has some walking difficulties and daily up and down that I have read about might be too much.

Thanks!

I found taxis in Lisbon to be plentiful and reasonably priced.

Agree. And some areas are not hilly.

There are also the fabulous "elevators" for great views as well as getting you up and down the hills.

Yes, there are a few " elevators" , cheap taxis ,and flat areas, but Lisbon is still the hilliest big European
city I have visited .

Public transport is varied and excellent, and taxis are cheap. There are trams, a metro system, funiculars and even an elevator. If you sleep on the flat you should be able to get everywhere else with no issues. There is a large flat area running north from the Praca do Comercio.

http://www.golisbon.com/transport/transport.html

http://carris.transporteslisboa.pt/en/home/

Staying outside would just add an extra journey, and the hills would still be there.