I have written this under Castillon, because Vall d'Uixo does not exist in the database of locations. It is approximately 15km East-Southeast of Castillon. Unless you are fluent in Spanish public transport, it will likely require your own transportation.
Check the website for exact operating dates, but the tours start roughly from 11am ~ 5:45pm, with extended hours in the summer. Each tour takes 45 minutes. Photography inside is not allowed, hence why I have only posted a photo of the river's map. Entrance is 8Eur if I recall correctly.
This cave has evidence of being inhabited more than 15000 years ago. But today, it open only to guided tour. The 2700m long passage is mostly accessed by paddle boat, but there is a long loop that you will walk on by foot until returning to the boat.
The rock formations and waterways are fairly impressive.
This is a picture of the Basilica of Our Lady of el Lledó, located in the outskirts of the town. It hosts the image of the Saint Patron of the town, Our Lady of Lledó, and is one of the biggest shrines in the province.
The basilica is surrounded by orange groves and you get there walking under a tree shadowed alley.