We will be flying to Granada three days before hooking up with the Rick ‘Steve’s Portugal tour. What are some things to do in Granada and is it worth the trip?
FYI: https://www.spain.info/en/destination/granada/
It's not for everybody but it might be worth it based on your interests.
Granada is definitely worth visiting. In addition to the Spain.info site, look at the things to do section of TripAdvisor for ideas that may be of interest to you.
Assuming you’re picking up the Portugal tour in Lisbon, Granada seems to be out of the way. There must be some reason you chose to fly into Granada rather than someplace like Sevilla that is closer to Lisbon. Go to Granada because there are things to see that are of interest to you and not because you think you should because others say you should.