Deadliest Cache

You can catch it here.

Before you start fishing for this you need to get the achievement Relics of a Fallen Empire.

You need to have the buff [spell=401577] to fish up the caches. The buff can be a bit buggy and get removed even when you are standing in the right spot at 54, 33 in Zul'Gurub. If this happens just run up the hill and then back down to the water and make sure you have the buff when you are fishing.

You can also only fish up one cache per day, per character.

I have found that the Mudskunk Aroma buff is less likely to vanish if you manage to start a cast while you have it. The invisible line that grants the buff is right between the bamboo "tree" and the leafy bush on the hill. Standing next to the bamboo you can easily cast into the water. If the buff wears off while fishing (which is unlikely), just run to the bush and back.