It begins at Exit 220 of Highway 400, south of the town of Parry Sound, where the road continues west as Hunter Drive to the former route of Highway 69 (Oastler Park Drive). From Highway 400, the route travels straight east to Orrville, where it turns north onto Star Lake Road. The route zig-zags through rugged Canadian Shield and thick forests, generally arching northeast until meeting the Nipissing Colonization Road north of the ghost town of Seguin Falls. The highway crosses the Seguin Trail, turns east and parallels it through Bear Lake, Whitehall and Sprucedale. The trail arcs south at this point, and Highway 518 continues east. South of Doe Lake, the highway turns northeast, while Star Lake Road continues east.