In the northern part of Darkshore, there’s a massive whirlpool known as the Maw of the Void. Alliance players can jump down into the whirlpool and complete Ghosts in the Dark which allows them to discover the secret of the Maw. I’ve heard that you can also get the [Going Down?] achievement without taking fall damage. Try it during Brewfest to get completely smashed and get the [Drunken Stupor] achievement.
As a Horde player, I discovered this gem sometime last year. Jumping into it starts a short cutscene of your toon being sucked into the whirlpool. You end up in the Bashal’Aran Collapse where a lone Cenarian Circle druid sits by the water’s edge.
Speak to Bielara to teleport you back up to the surface. Oh and if you’ve ever wondered if the huge whirlpool in Stranglethorn Vale did something similar… it doesn’t. All I got was a repair bill :P