The scariest roads I've ever been on were Moe-Rawson Road, and Walhalla Road. The two roads that lead up to Walhalla. The speed limit was either 80 or 100, but there were many sections where it was blind twists and turns, and no guardrails guarding a very steep drop off the road. It would've been completely unsafe to drive at 80. Even 40 felt like it was pushing it. Going up is okay, because you're on the inside so you'd only be rammed into a mountain. But coming down (back towards Moe), all it would take to be flung off the side of the mountain is somebody doing 80 while coming up and not being in their lane (probably impossible at that speed with turns that tight).
That's really the only road I've automatically felt unsafe on as a passenger. Oh, and at the start of the road there's a very bright red sign that says something like "U TURN FOR LAST FUEL. NEXT SERVICE STATION 300KM" or something like that