Assuming that you start out from Bad Münster am Stein there are two possible ways to start the trail.
Probably the most interesting part of the route is the crossing of the Nahe river by ferry. From downtown Bad Münsterget to the Nahe river where you easily distinguish the boathouse. The ferry is a medium sized boat that is connected to a chain across the river. The ferryman drags himself, the boat and his passengers along by pulling on the chain manually.
In principle the ferry starts every half hour but since the river is only some 20m wide the ferryman will get you regardless of any schedule. Lhe last ferry crossing is at 18:00 o'clock. The ferry jetty on the southern side is directly at the entry of Huttental where the ascent starts.
Nahe River Bridges
The second way to get to the trailhead is by crossing the river on one of the three bridges (pedestrian, road and railroad). Head along the road into the Alsenz river valley for some 1km. Keep on the west side of the river. There is a campground at the intersection of both rivers. Right after you have reached the end of the campground turn left and follow the signs to Rheingrafenstein. This trail is a panoramic trail that heads along some 100m above ground so that you meet the ferry trail a little above the jetty.
The trail winds along the short and narrow Huttental. The valley ends and from there on a moderately steep hiking trail winds up towards the rock and castle of Rheingrafenstein. It actually is part of the moat of the castle. Several cave entries tell of the mining history of the region where formerly silver and mercury have been explored (there is a visitor's mine just a couple of km to the west of Rheingrafenstein.
When you reach the castle you are only halfway up the rock. Due to the small usable area on top of the rock the castle spreads quite a way down. you reach the "drawbridge" nowadays a fixed one) where you can turn left and start climbing the castle grounds. After some three or four floors you reach the remainder of the step towards the watchtower (Bergfried). Go up here (take care of your head, the stirway's low) and you reach the uppermost plateau of the rock. Enjoy the vertical views down to the Nahe River
Just hiking equipment if you only want to reach the top without climbing the walls.