I've taken another good look at the maps of the Miura-toge Pass portion of the Kumano-Kodo trail, hoping to get a better idea not just of the terrain, but of how the terrain changes and also the amenities available along the route.
From the Mandokoro guesthouse to the trailhead is about 0.7km (0.45mi) travelling mostly along the Route 733 road. (
Link) This is quite a narrow, winding mountain road, with a steep mountain side to the left and a steep drop down towards the Kanno River on the right. (
Link) I've got to be honest, even this relatively short section of road looks pretty dangerous if a car came speeding around one of the corners.
You then go off the road at a point that appears to be marked for the Kumano-Kodo trail (
Link), passing a number of houses towards the Kohechi Funawata Bridge which crosses the river. Google's images of the area were last updated in 2013, at which time there appeared to be a lot of building work going on around the bridge and the river. I'm not sure what it looks like now. (
Link) This is as far as you can get on Google Maps because after that you're on the trail in the mountains and the forests.
According to the official trail website (
Link) you quickly climb from 400m (1300ft) to 1100m (3600ft) over a distance of 4km (2.48mi) to reach the peak of the Miura-toge Pass. The route is rated 4.5 out of 5 because it's VERY difficult. Steep embankments, ravines, narrow paths, etc. At times you're almost rock climbing.
At 3km (1.86mi) into the hike there is the Sanju-cho water spring and other ancient remains and markers. It's possible that if you were to go off the trail for any reason, this would be where you'd do it. But it appears everything is marked so I'm not sure how you'd get lost.
The trail is about 18km (11.18mi) from Mandokoro to Pattie's next stop in Totsukawa. The peak of the Miura-toge Pass is only 4km (2.48mi) into the trail, although it's a very difficult hike to get there. At the peak is a toilet and a covered shelter, so the chance that Pattie had to step off the trail for a call of nature is perhaps not high, although still possible. At the peak there is also a forestry road which could potentially be used if you had reason to step away from the trail--or if somebody wanted to abduct you.
I won't go further at this point because TBH, I doubt Pattie even made it to the Pass. But the whole route to that point is just mountainous forest with a few streams. All sight-seeing spots are clearly marked. You could easily get lost if you went off the trail but I can't really understand why anyone would.