Coming from the Bowerstone Castle entrance to the Market, enter the very first house on the right. You’ll find the key out back.
This key is behind the fish stands, down the stairs on the side of Bowerstone Market that leads to Millfields.
(Hideout) You can access this area late in the game. On your way down through the hideout, look out for a door to the right of the glowing trail. Opening it will lead you down into an area where you’ll spot this key inside a cell.
Bowerstone Old Quarter (2 Silver Keys)
Coming from the lake area, head left along the city wall until you reach this key.
Turn down the left street after passing the vendors and after climbing some shallow steps you’ll see the Nightshade House here. Inside on the second floor lies a silver key.
Brightwall Village (5 Silver Keys)
Follow the wall to the left of the library entrance and you’ll see this key hiding among some rocks.
Just behind Bernard’s house (the one with the chicken coop) you’ll find a silver key.
Just outside the village there is a small property called the Spurious Nuttock. Take the nearby stairs to get under the bridge and find this key.
(The Reliquary) In the area near the skeleton, use your fireballs to light all of the un-lit torches. Doing so will open a secret door.
(The Reliquary) After you nab the key listed above, make sure to go right instead of straight at the junction pictured. You’ll eventually reach an area to your right with a switch. Flipping it will spawn some hollow men. After defeating them, you’ll see a staircase appear across the room. You can figure out the rest!
Driftwood (2 Silver Keys, 1 Gold Key)
As you make your way to the Hobbe camp on the leftmost island, you’ll come upon this area where you must leap off the ledge to grab a silver key. It’s on the left part of the island.
On the large center island there is a small cave. Go inside to find this key.
Once you’ve competed “An Island Getaway,” “Pest Control,” “Gift Wood for Driftwood,” and “An Island Getaway,” come back to Driftwood. If you’ve waited long enough (just complete an odd quest or two) there should now be bridges connecting the islands of Driftwood. There is a flit switch on the rightmost island that is now accessible. Hit it and follow it around Driftwood. You won’t be able to get to it at all of the different spots unless you completed all four of the quests above.
Dweller Camp (1 Silver Key)
Enter through these double doors and turn right to find the silver key. You won’t be able to access this area the first couple of times you visit the Dweller Camp, as the doors will be shut.
Mercenary Camp (1 Silver Key)
Under this structure, near the where the dogs come out of their cages to attack you.