The H.A.M. Store rooms is a secret dungeon inside the H.A.M. Hideout. It is only accessible to players who have progressed halfway through Death to the Dorgeshuun. The secret entrance is located just south of the podium in the main hideout. The stores are patrolled by guards, though after you have finished the quest, they are not aggressive (i.e. they will not attack players unless attacked first or spoken to).