If the beach gets boring (which would be very surprising), there are a world of activities to dive into in Colera:
Take a stroll through the small farmers/artisanal market every Monday, where you can find fresh fruits & vegetables, honey or cold cuts. There are also less traditional stands with souvenirs or small town “lingerie”.
Or walk down a beautiful path post lunch that follows the coast offers amazing views. Just ask how to get to it at the Mont-Mercè.
Or if you feel like a trek and are keen to observe how people lived a 100 years ago, visit the abandoned village of Molinàs. You can walk or take a bike there but remember to wear appropriate footwear.
There is also a padel tennis court, managed by the town council and available for a reasonable price (for times you’ve had one too many tapas).
For a cultural experience, visit the Dali museum in Figures. You can go by car or take the train at the station in Colera, which is just 5 minutes away from the Mont-Mercè.