I feel it's finaly my time to contribute. I've seen a lot of posts about swimming in the air in outlands, but I've found a way to swim UNDER outlands...but, first lemme start with how I discovered this.
I was playing on my new warrior, doing some of the Zangarmarsh quests. The Umbrafen village quest in particular. I engage one of the Umbrafen Witchdoctors, who summon a totem that casts "Terrify." This is a fear. It feared me under the world. I was able to swim around for a bit before I fell to my death. This may have little or no use, but I did find it fun. I've only been able to do this once. SS below.
(Sorry if this post sucks, this is only my second post >.< flame away)