On a rainy afternoon in La Manga, you can visit the Mar Menor Museum. This museum showcases the history, culture, and ecology of the Mar Menor, a unique saltwater lagoon located near La Manga. You can learn about the diverse marine life, the importance of the lagoon for the local ecosystem, and the traditional fishing practices of the region. The museum also offers interactive exhibits and educational programs for both children and adults, making it a great option for a rainy day activity.