Pimmu is a medium-sized cave in the Boethiah's Spine containing smugglers. Head out of Alt Bosara, past the Telvanni Waystation and across the bridge. Stay on the path as it twists and turns until it heads due west. At that point, break off to the north and follow the coastline. Pimmu is on the western bank at the end of an inlet.
The cave is crammed with crates and barrels containing the gang's ill-gotten gains. Much of the loot is found in the southeastern chamber, which is also where several of the gang sleep. Judging from the copy of ABCs for Barbarians by one bed, it seems one of them is taking small steps towards improving him or herself.