Dark Iron Baby Booties

Farming tips:

1: ignore comments about farming keys outside. it's impractical and a waste of time.
2: first go left through the gate and clear the hallway around Bael'gar
3. chances are you will be a bit short. at this point you can go back to the entrance, clear detention block, or the circle that takes you pass the Ring of Law. In some rare cases you may have to do both. In some extremely rare cases you might still not have enough (you need 12 keys) --- at this point I recommend just cutting your losses and opening the coffers with what you have and resetting. farming that 11th or 12th key is not time efficient.
4. if you're a looter, empty your bags completely, bring a portable mailbox, and take advantage of the vendor at the entrance. looting greens can be very profitable here! do not open gem bags from the coffers, leave them in your bags until you're at a mailbox/vendor.
5. the dark keeper is a waste of time -- if he's in the Hall of Crafting, it's directly to the right when you leave the coffers, and you could pick up an extra green or two if you want, only adds about 60 seconds to a clear. It's a hike to his other 3 locations, I don't recommend it.

quickest ways to BRD:
Direbrew Remote (1hr CD)
Warlords of Draenor Challenge Mode portal to UBRS (8h cd)
Mana Poof BRD Pet Battle Dungeon Teleport (no CD, but only from Legion Dalaran or Boralus)

The 12 Relic Coffers are all located in "The Black Vault" which is where [npc=9041] is located and shown on your map. Unless you are very familiar with the twists & turns of this instance, then after you have the keys, recommend returning to the entrance and using the Mole machine there. Select the option "Into the Domicile", then out onto the semi-circular balcony & into the vault.

Dark Iron Baby Booties drop from opening relic coffers in a specific region of the legacy dungeon called Black Rock Depths.

For those who do not know, or maybe forgot because it has been a while:
The Black Rock Depths dungeon entrance is inside a cavern located between Black Rock Summit and The Searing Gorge.
Once inside the dungeon, use a strategy to loot the keys and then open the coffers to try for the Dark Iron Baby Booties.

There are 12 coffers in the treasure vault and each one requires a key to open it. You do not need all 12, but the more the merrier.
Any more than 12 keys will be lost when you exit and come back into the dungeon. If you accidentally leave the dungeon, you will
lose all your coffer keys.

You can use the dark iron teleporter (mole machine) near the entrance to travel to the domicile, which is near the treasure vault.

Before you do, try to collect 12 keys first to maximize your chance of getting the Dark Iron Baby Booties.
Relic Coffer keys drop randomly from the elite dark iron dwarves throughout the dungeon.

Strategy includes:
Circle the Ring of Law, circle the detention block, go down the middle of the detention block. Traverse the hall from Baelgor
to the opening of the chamber that leads to the dark forge. Use the mole machine to go past the Grim Guzzler to kill the two
packs of elites.

It took me anywhere from 15 to 25 minutes to get 12 keys, so a full run was almost 30 minutes. I got Dark Iron Baby Booties on
my 5th run. So it took me a little over 2 hours to get the item.

Good luck, and I hope you get it sooner than I did.