Unfortunately, as an AI language model, I do not have browsing capabilities to access external sources on the internet. However, I can provide you with a general summary about parks in Iowa, which could include Rio Valley Park.

Iowa has numerous public parks that offer various activities and attractions for visitors. These parks provide opportunities for hiking, biking, fishing, boating, camping, picnicking, and other outdoor activities. Some of the notable parks in Iowa include:

- Effigy Mounds National Monument: This park is located in northeast Iowa and features more than 200 prehistoric Native American burial mounds, including animal-shaped effigy mounds. Visitors can hike on several trails and learn about the history and culture of the Native American tribes who built the mounds.

- Maquoketa Caves State Park: This park is known for its unique karst topography, which includes more than a dozen caves and underground passages. Visitors can explore the caves (with proper equipment) and enjoy hiking, camping, and picnicking in the park.

- Pikes Peak State Park: This park is situated on a bluff overlooking the Mississippi River and offers scenic views of the river valley. Visitors can hike on several trails, visit the Pikes Peak historic tower, and watch for bald eagles and other wildlife.

- Ledges State Park: This park features unique sandstone cliffs and rock formations that provide scenic views and interesting geological formations. Visitors can hike on several trails, swim in the Des Moines River, and camp in the park.

As for Rio Valley Park, there is not enough information available on the internet to provide specific details about its attractions and features. However, if the park exists, visitors may want to research its location, amenities, and activities before planning a visit. The best time of year to visit Iowa parks generally depends on the season and weather conditions. Spring and fall are usually mild and pleasant, while summer can be hot and humid, and winter can be cold and snowy. Visitors should check the park's website or contact the park office for more information on seasonal activities and conditions.