The Classic Travel Quandary: Checklist in Lisbon? or Linger by the Sea?

On our recent trip to Portugal we chose to stay in the lovely seaside town of Cascais, 40 minutes outside of Lisbon.  We had a pretty swish HomeAway overlooking the hills and sea of our quaint fishing town.  My favorite part of the home was that we could depart on foot and hike for hours in the hills in front of our house exploring the various trails that criss crossed the cliffs. BUT, we were in Portugal and you can’t go to Portugal without seeing Lisbon, right?