Another very scenic and curvy road is Iron Mountain Road, that connects the Mount Rushmore area and Custer State Park.

An interactive map:

Bison:

There are three narrow tunnels on this road:

One-way road:

Another tunnel:

Pigtail loop road:

Low narrow tunnel:

The third tunnel:

This tunnel has a view of Mount Rushmore:

Pigtail loop road:

One-way roads:

Mount Rushmore view:

A fun drive.