Underwater, no one can hear you scream.
We once again visit an old favorite instance, this time the Blackfathom
Deeps in Ashenvale. The instance is an ancient temple dedicated to the
Old Gods and now occupied by the Twilight Hammer cult. The cult has
joined forces with the naga and corrupted satyr in the area to occupy
the temple and protect and worship the creature Aku'mai.
The Blackfathom Deeps (BFD) are meant for characters level 20-30ish. You can continue to make loot and experience runs through BFD to about level
32, but by that point the experience gains are hardly worth the effort.
Give the guide a look at the Ten Ton Hammer WoW site.