A lonely castle stands atop a rocky outcrop just beside the highway between Beirut and Tripoli. You'll see it a short while after passing Batroun but just before the tunnel. The defensive castle is probably used to defend the route from Tripoli to Beirut during the old days.
As you pull off the highway, stop by a small ancient rock bridge. Cross the bridge and walk a short distance and you'll find the entrance to the castle grounds. You might need to get someone there to open the doors to the castle.