From Rogue River, OR, take the Rogue River Hwy (Route 99) east to Gold Hill, OR. From there get on Route 234 and take that northeast till it runs into the Crater Lake Highway (Route 62). Take a left on to Crater Lake Highway and head north all the way up to Crater Lake National Park. Enter the park and head up to the lake by way of Munson Valley Road.
You travel along the Rogue River, through tall pine tree forests, and end up at Crater Lake which by itself is worth the trip.
Roads are mostly flat or curvy. A couple of sharp turns along the way. Mostly two lane roads in good shape. You do go through a snow zone so it could be closed in winter.