Thanks to Craig for showing me these yesterday. There are three tunnels close to each other. The two outer tunnels are the usual shape and size for people, and the middle tunnel is larger. None of them go back more than a few feet into the hillside, as though they started digging then decided against it.
The map marker's location is approximate, but if you follow the concrete path around the 'giant golf ball', you can see these just a few feet away from the railings, down the slope.