Throughout the history all the civilizations that passed in the area of the Dog River (aka Nahr El Kalb) left a trace. The Romans built a bridge, but it was destroyed. However you can still see the base of the Roman bridge at the northern side of it. The actually present bridge is Arab. It was built by a Mamlouk Sultan during the 14th century. You can read it on the Arab Stele next to the bridge on the other side of the paved road.
The Bridge was restored in the 1800s by Emir Bechir.
If you look on the mountain facing the northern side of the bridge you can see the old Roman aqueduct that used to deliver water all the way to Beirut! It is still in use with running water in it.
Note: When the river is dry, you can walk under the bridge so you can see it from below. It is really impressive.
DON'T FORGET TO TAKE A WALK IN THE ANCIENT SITE ON THE HILL NEARBY TO SEE THE STELES!
The cache is hidden at the northern end of the ancient bridge. You can park your car right next to the bridge on the road side, take a walk and cross it to the next side. There, the cache's location has been altered due to renovation works, thank you ainars58 for taking care of replacing it!!. You can read the comments to have an idea about its location ;)