Once on Main Ave N / MN-139 from Minneapolis, what road do you take next?

The correct choice for navigating from Main Ave N / MN-139 towards Niagara Cave involves taking County Road 30. This route is significant as it leads you towards the destination effectively while also connecting with the necessary roadways to reach Niagara Cave. County Road 30 is designed for efficient travel through the area, facilitating access to rural attractions such as the cave.

While other options may represent real roads in the vicinity, County Road 30 is the most direct and appropriate route that aligns with the best-known paths to Niagara Cave. Understanding the layout of the area's roadways is crucial for navigational accuracy when guiding visitors.