After completing a number of jobs in Markarth (5 or so, I think...), Delvin will have this "Special Job" for you. He wants you to go see a silversmith named Endon to try and sway his family back to our side. Go find Endon (who I found at the Silver-Blood Inn) and he'll tell you that the reason that he needs your help is that he ordered a special silver mold that was stolen from a Khajit Cravan. The people that took it are bandits led by a woman named Rigel Strong-Arm, and they can be found at their hideout at Pinewatch. He wants YOU to get it back for him.
Note: I'm going Rambo on the bandits, but you could sneak through the whole thing if you wished: there ARE multiple paths near every bandit after all!
Pinewatch is just east of Falkreath, so make your way there. Since these are bandits and my killing-instincts are getting rusty from all this thieving, feel free to kill them on sight (they'll attack YOU on sight). Once you enter the cabin, you'll see that it LOOKS LIKE a fairly small place. Go ahead and kill the man named Rhorlak here: trust me, he's in on this and deserves it. Head downstairs and you'll hear wind in a tunnel. That's easy to explain: there is a tunnel behind the bookcase here, and a button on the wall to the right will open up the path.
Head down and kill the two bandits on the walkway. If you go straight, there is another bandit in that room (there's also an EXPERT locked supply door to the right as well as a chest on the floor down below). Go left now and you'll be in a new area. Kill the three bandits here and look out for a chest up on one of the broken-down pillars and proceed onwards to find one more bandit by a door leading to the Pinewatch Bandit's Sanctuary. Enter.
Kill the three bandits sitting at the table and loot the chest here. Head up the nearby ramp and through a tunnel to kill another bandit. From here, go up some stairs and open a wooden door to find another bandit patrolling a Draugr filled area (she's killed all the Draugr already). Go pick the RIGHT door (it was a NOVICE lock for me) to find a lot of goodie, including a STONE OF BARENZIAH! The chest here is trapped, just FYI, so open it from the side.
Continue on and you'll see a warning on the wall. Seems like Rigel has had some people try to break into his treasure room. Well at least we know there will be traps! Continue on to the bedroom and kill any bandits sleeping. The rest will be in the dining room next door (You'd have to be invisible to skip being seen here!). You'll be in for a fight as you kill them, as there can be 3-4 enemies here. In fact, Rigel is in a bedroom maybe 2 rooms away. She was SLEEPING for me (meaning I could pickpocket her or get in a sneak attack) but I imagine that it is VERY possible for Rigel to join in on the dining room fight, so be extra careful and use potions when you have to (or even save before hand just to be save).
Either way, once you have Rigel dead or pickpocketed you'll have the key to the treasure room, which is even further in. Open up the wooden door then the iron door. There is a floor plate RIGHT before you step out onto some logs, so be sure to avoid it. In fact, just avoid ALL the floor plates as you continue to the next door. Heck, even that door you should open and wait as a mace will fall down once you open it. The treasure is now in front of you though! Be careful of the floor plate by the pile of goodies and loot to your hearts content before using the door nearby as a shortcut out of this place!
Go outside and return to Endon to give him his silver mold. He'll be very happy and will reward you with a pair of Elven Boots of Strength (which are verily kick-ass) and will volunteer his services as a fence. Return to Delvin to let him know you are done with this mission.