Bloodborne

This is a secret area you can unlock. After you have killed the Blood Starved Beast a extra passageway opens up in the Cathedral Ward. There is an elevator here and it leads to an entry to another tower. Follow the route in the video and the trophy unlocks as soon as you enter the old Workshop.

Everything after the second minute of the video is just me collecting the items available there after the trophy had popped.

The Source of the Dream trophy is awarded for discovering the Abandoned Old Workshop, one of the first armories ever used by the hunters of Yharnam. You should recognize the area once you discover it; it is almost identical to the garden and workshop of the Hunter's Dream.

The Old Workshop can be reached once you discover the Healing Church Workshop, which itself can only be accessed once you slay the Blood-Starved Beast of Old Yharnam. Once you have, start from the Cathedral Ward lantern in Oedon Chapel and leave through the right-hand door (which is locked until you kill the aforementioned Beast). Take the elevator up to the workshop storeroom but watch out for the wheelchair hunter armed with a gatling gun.

Head to the left through a door and across to a neighboring tower, which formed the core of the Healing Church Workshop. Snipers will be firing at you from the second floor but instead of heading into the tower chambers, follow the landing around to the right; when you come to a wide gap in the walkway, drop down to the landing below and continue around the tower. You'll find an entry into the tower, emerging at the top of a wide, exposed shaft dropping down into darkness. A few flimsy wooden bridges and platforms provide your only means of descent.

If you want, spend some time actually exploring this tower and make the descent to its bottom a few times, to get the feel for it. As you do, you'll notice a ledge about halfway down with a closed, ornate door. You want to reach this door. Starting from the top, by the entrance, you want to drop down to the left, landing on a small platform above the door you're aiming for. A pair of ropes lead down from the entrance platform to this tiny ledge. If you make the landing, you'll take a large chunk of damage. Heal up with some Blood Vials as you will take more damage once you drop from this landing down to the landing with the door.

Once you've made it, open the door and proceed down the steps. You'll emerge in the gardens of the Abandoned Old Workshop.

For those who find video guides more helpful, take a look at this guide provided by PS4Trophies:

This is an easy trophy to get if you know where to go. To unlock the door leading to this area, you must have first killed the Blood-starved Beast. Once you do that, travel to the Cathedral Ward and follow the path in my video in order to unlock yourself a sweet silver trophy!