This video guide shows how to get five hidden merchant chests through the walls of Vlindrel Hall. This is the highest mansion in Markarth that you eventually get to purchase. Often there's a glitch where the house isn't available from the usual Jarl and steward so one must progress through the main quests until the quest "Season Unending". It is recommended not to do the civil war quests until all other quests are finished as this will prevent further glitches. A platter and a few do not delete chests are required to acquire these unknown merchant chests. This particular wasn't meant to be gotten until later in your adventures as it really can't be purchased until level 20 however may take longer than that if main quests have to be completed.
