Solitary Colossus

While the Solitary Colossus may appear unreachable, it does not need to be attacked with Junundu Siege - just approach the side of the rock platform on foot and use something like Immolate on it. As it is only level 1, it is pretty easy to kill. Once it is dead, you will be able to walk onto the platform - and onto a new rock bridge which takes you across the chasm to claim your reward.