Group Instance in North Ro.
To get to this instance, go to the south portion of the zone in the center. There is a sand pit. Click on the ground to enter.
The adventure window says this about the instance.
The Elite of the Jeweled Guard and the Geomantic Compact in Takish-Hiz have captured one of our brightest minds, Ambassador Plauh. They are trying to learn all of the magic of Norrath that they have missed being buried in the sands. They have not succeeded yet, so there is still time for a rescue. Get to a quicksand pit in Northern Ro to enter the city and work your way to Ambassador Plauh.