Where in the Park is this?

Starting on Cathedral Road from Cainville, about 17 miles each way. In 17 miles you'll see a side road on your let that leads to Glass Mountain and the Temples of the Sun and Moon. First up, you'll see a weird-looking mound before reaching the Temples. This is Glass Mountain. From here you see the Temples, so go explore! Drive back out to Cathedral Road, and return the same way you came.