Morella's compact size means you can cover most of the major sights on foot in a day — but it rewards a slower pace. The castle is the obvious centrepiece, accessed via a steep path from the old town. The Basilica de Santa María la Mayor is the architectural highlight, with its extraordinary spiral stone staircase. Walking the medieval walls is one of the best free things to do in the region.
The Els Ports Natural Park surrounding Morella offers hiking through limestone gorges, waterfalls, and dense oak forest — good for a half-day if you have a car. The area around Morella also has several historic villages within 30km that make worthwhile short excursions: Forcall and Olocau del Rey are both well-preserved examples of the same highland medieval landscape.