Krak des Chevaliers is an intimidating Crusader fortress in the hills close to the Syrian border with Lebanon.  The Krak is one of the most important structures of medieval military architecture in the world and was the headquarters of the Knights Hospitaller during the Crusades.  Built in 1031 and expanded by crusaders to its present impenetrable state, the fortress is monstrous with outer walls that are 100 feet thick.  Numerous sieges were undertaken to capture this strategically positioned castle by hostile Muslim armies, yet none succeeded.  There are passages leading to stairwells that descend deep into the pitch black depths of the castle.  Regular tourists and guides never venture to these isolated tunnels, watch where you step, if you make a wrong move down here it can be fatal.