At the very least go to one of the many lookout points, such as Eduardo VII Park, wander around and have a nice meal & coffee if going downtown is too much for your spouse.
Thought going downtown to wonder some shops, stroll the streets, eat some pasteis de nata, sample some Iberico meats or maybe an octopus dish (all things I do when in Lisbon) is more appealing to me the calmness of going to a park, having a bite, coffee or a nice wine isn't bad either.