I have just finished spending my whole night playing this but I figured out how to get the second Shrine Maiden Statue to open the 4th layer without using the blasting bomb in the Courtyard so I must share (I was almost convinced you could get locked out of the layer entirely with an incorrect use of that item). You're going to need an invisibility (Clouding Eye) potion and maybe a Potion of Poisonous Bugs too.
If you take the teleporter to the 2nd Layer, and then take the teleport trap above the stone in the room with the 4 seals, you'll end up in a pretty central feeling area of the Layer. Then go southwest from there and cross that bridge until you reach a campsite, without leaving this room, head north from the campsite and cross that bridge before entering into a gate. This is where you activate the top right seal, the trap temple (Or Unclean Temple, but you get it).
Go forward until the first fork, then take a right into the room with two jail cells below you and a monster ahead of you, then lockpick that door into the teleport trap moving around the spikes. Now, and this was a revelation for me, walk OVER the spikes to the right. Unlike the vast majority of games like this, stepping onto traps will hurt you, but never move you, so you can just walk onto the spikes and then walk off to other side. This will be the only required trap check, but you should probably put on the Trap Knowledge skill if you have it, because these dual traps are the theme here. Lockpick that next door, you've got to be quick to not get teleported, but the teleport traps become stationary after they get you once, and read that diary, or don't, whatever. Pop the invis potion, kill the monster manning the cannon, and the rest is just more typical trap and teleport timing.
Small note to save you some time, when you enter the room with a cannonball line coming right at you, just walk off to the side to get down that path, you'll then want to go down again before heading towards the upper right. You've got to manually deal with another monster to progress. Get out of that room and your Shrine Maiden Statue is right there for you, though keep in mind the LADDER IS A ONE WAY TRIP so grab everything first. You'll be dropped into the top right of Heisui(?) Town, but just walk left and you'll get out no problem. You'll have to navigate that next room too to pop the Return Stone, so get ready to save scum lockpicking or bring a Potion of Poisonous Bugs too.
If you're wondering where to use this statue, search the thread for how to get back to the tutorial and you'll be in the right general area (Southwest 1st layer). When you find the red monster with synchronized openable bars on both top and bottom, you're almost there. Also quick note that I did this at lvl 167 and didn't exactly have an easy time since traps do %HP damage, so make sure to be rested and stocked up.
The guide is over, I will now be yapping. Having used a save editor to get myself another blasting bomb so I could explore the other end of things, I did learn of a pretty helpful one time use item that you get if you do the Courtyard bomb, so that's probably still the play if you have the choice still. I imagine, hope, pray, plead even, that the item is accessible in other ways, but it wouldn't be the first time this game has tested me, clearly. I will probably put a review together when I finally get the good ending and start NG+ (Been doing Prayer but I've got some crazy crit skills, so Skill focus next), but my general thoughts are:
++Very souls-like map design
-Souls-like NPC questlines (the memo system works great, just give me more of them)
++Fatigue&Time help break up the endless exploration and add some real danger(for a virgin run at least), even to save scummers like me
-Those lockpick %'s are a fucking lie
++Unique art for every weapon, shield, hat and body (doesn't affect H-scenes)
-Should probably list Bunny and Cooking EXP somewhere (they aren't too expansive, I just want to know)
--False shota (had my hopes up)
++Souls stats, weapon scaling, flask system (even little hint text during level up for what stats do)
+EXP gain based on level for noncombat activities (helps keep the non-dungeon content impactful)
+(Sometimes) viable stealth, I've actually managed to lose an enemy a few times
And that's a scroll bar so I'll shut up now, very good game except for the bad parts, as always.