As I get deeper into Bloodborne, I start to realize that there is a shit-ton of hidden bosses and areas. Far more so than in any previous Souls game.

I thought we could use this here thread to tally up the areas we've found and how we've done so. Let's try to mainly talk about larger pieces of content here as opposed to "this nook with an item I found when turning 720 degrees after greeting a corpse that ragdolled into a rude position". Basically, this is larger pieces of content. You guys are free to share secrets you find in here, as well as smaller areas, but let's leave small stuff to the other threads.

Areas

For reference, these locations all seem to be larger than the Painted World in Dark Souls.

Forsaken Castle Cainhurst - This an entire, large area with a unique boss encounter, as well as a covenant. You can reach it by going to the Forbidden Woods, reaching the small village with the pitfalls, and then heading up to the left above the town. There's a tunnel that leads to a lake, at the far end of said lake, there is a ladder long enough to have me singing "Snake Eater". The end of that ladder has a short-cut to the clinic where you start the game, as well as a path that leads further into said clinic. In there, you'll get a cutscene and fight an NPC. Doing so will net you the "Invitation". Once you have said invitation, go to Hemwick Charnel Lane, the big open area before the boss in that area and stand next to a larger stone marker. This will trigger another cutscene.

Nightmare Frontier - Go to the Forbidden Woods yet again, to the same spot above the village, and talk to the NPC sitting in a window. He will give you a "Tonsil Stone" (yuck). Now teleport to the Grand Cathedral where you fought Vicar Amelia, and head to the left. At the far end of that passage way is a big temple. Stand at the entrance of the far door (it's locked until you beat a later boss, prior to which you should not be doing this content) and he'll summon a gateway. With the Tonsil Stone, you'll be able to pass through said gateway into the Nightmare Frontier. A place of asshole slugs and asshole yetis, with a really big asshole boss. Do enjoy. This boss also drops an item that unlocks a brand new type of Chalice Dungeon.

Upper Cathedral Ward - Head on over to the Yahur'Gul Chapel. From there, run back up the stairs to the plaza with the elderly ladies and the spider shooting laser beams at you. On the left side, there is a opening in the fence which allows you to drop down onto a balcony. Do so and then head inside, there you'll find a key after dropping down again. Now, go to the Cathedral Ward, use the door on the right and head up the lift. Clear this area and head to the top where you'll find a badge for a really, really great weapon and a door that was previously locked. Use this key, bam. Here's a brand-spanking new area with two new bosses and a covenant.

Bosses

Other than the four bosses in the hidden areas, I've only located one other.

Darkbeast Paarl - This one is pretty easy to find. Go to the Yahur'Gul Chapel, and head on downwards into the cathedral. Here, take the stairs downwards until you reach the lowest level. You'll find a type of werewolf patrolling these areas that you do NOT want to mess with. Make your way through this area and you'll find a small opening in the wall, leading outside. Dropping down will put you on a ledge. Navigate said ledge into a courtyard where the boss will appear.

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These are all I've found so far. I'll update it if I locate anything else.

You can fight Paarl very early in the game (Actually that seems like the intention) if you want to via Bagman, probably the coolest looking boss I've ever seen in anything (though the fire dog of chalice land is pretty sweet too).

@fredchuckdave: I dunno. Moon monster is kinda rad. As for design though, I think that the game peaked at Father G. Nothing has made the same impression as he has yet.

@viciousbearmauling: I lied there's a guy way down in the Chalice Dungeons that looks fucking ridiculously awesome, also it's a great fight.

@fredchuckdave: Are the Chalice Dungeons worth doing from a lore perspective? Is there a tangible bonus to my understanding of the game world by doing these?

@oldirtybearon: I believe each Chalice description has a little bit of lore to glean, also there might be some "rings" (can't remember what they're called) that you can only get down there, in addition to a few armor sets/presumably the coolest weapon in the game. Also don't you want to meet this guy and have a chat?

@fredchuckdave Is he just Paarl Again? You can tell me.

@oldirtybearon: You also get like 20 times as many souls as you would get normally when you're really far down, granted there's a lot of difficult rooms and so forth. I also got a Great One's Cold Blood in a Chalice Dungeon, not sure if they exist in the main game (there's probably one somewhere). I imagine it's just a Great Soul of a Hero but it does have different lore than the other soul items.

@crembaw: Nope, totally unique fight. If it was Paarl it would be called Paarl (this is not just me saying something obvious). Also you should be able to judge size from the picture, Manus/Flamelurker/Alonne fans unite.

@do_the_manta_ray: There's another secret boss in the main game (that's maybe too spoilery for a spoiler thread) and there's a whole shitload of bosses in the Chalices, some of which are unique and others that aren't, some that have varied attack patterns/behaviors when they're a boss vs being a regular enemy or they wield different weapons and thus have different attack patterns that way and so on. Also terrain matters.

@oldirtybearon: I can now say for sure there's an extremely important lore reason to be doing the Chalice dungeons.

@fredchuckdave said:

Good to know. I just finished the game and I'm eager to dig through everything I missed the first time around.