This guide is mostly for myself, but it may be useful for others. There are some hidden things in the house worth finding but you will not know about them unless you are very meticulous with your checking of objects, pay close attention to the texts, or you look up the fandom wiki. Franky, I hate using that wiki because of all the ads, so I'm copying a bunch of stuff from it to this guide. I try and verify each thing before committing to it though. Hope you enjoy. And obviously, if you want to find these things yourself, spoilers.

You can access some extra lore by clicking the center of the title screen upon booting up the game. Just click the librarian.

Memories are a necessary part of progressing in the game, where by helping you master books, boost helpers, or upgrading your skills. So having an easy way to collect certain memories will be essential to your game. Here are some repeatable memories you can get by simply observing items around the house. [Note: I am not counting craftable memories or memories you get from conversations]

Common memories:
Most art: sight (1 lantern)
Most furniture/weapons: touch (1 forge)
flowers: dissect for smell (1 nectar) [will consume flower]
food: eat for taste (1 grail) [will consume food, obviously]

Uncommon memories:
discard item via well: sound (1 heart)
discard penny via well: satisfaction (2 grail + 1 heart)
discard item via sea: loss (1 edge + 1 winter)
discard penny via sea: Impulse (2 moth + 1 Nectar)
Severn Chamber: Nighted Chair. observe for fear (1 edge + 2 scale)
Violet Chamber: Chair of Challenges. sound (1 heart)
dueling hall: red quarterstaff. Smell (1 nectar)
Cell-Long: weapons. observe for contradiction (2 edge + 1 moon)
Yellowing Newspaper (check containers): observe for Occult Scrap [will consume paper]

Additionally, every book contains a memory you can repeatedly collect by rereading it. It's different for each book, though.

To be clear this is not connected to House of Light. Some of the people who visit the library have written some of the books you will have, and will have special gifts for you if you present them with these books. As a bonus they won't even leave after being shown these books and will remain for whatever business brought them here.

Dr. Arun Peel:
Collected Hush House Lectures. Provides Wormwood Dream
The Flayed Tantra. Refuses to interact with it.
The Radical Measure. Will buy the book for a silver spintria
The Victory of Crowns.

Fr. Stanislav John Schaller:
Deaths and their Evasions. Provides Edicts Liminal lesson
Singlefoot Songs.
The Devoured Tantra.

Mr. Eshan Fekri:
Fekri's Herbary.
The Sea Does Not Regret.

Hokobald:
My deeds, my powers, my achievements, and the injustices perpetuated against me.

There are a couple of hidden compartments that can be found around the house that may house a few interesting items.

Librarian’s quarters: left of fireplace, below curtain. Contains book
Watchman’s Tower: First Floor: Below the pillar between the windows. Contains gervinite
Westcott Room: Left bookcase, top shelf, just to the left of the scroll slots. Contains Black Dove wine

Many objects can be found if you know where to look, or how.

Dig through bushes or explore the sea. Hush house key
Grand Ascent- Ground Floor: Delightful Repose. Bronze Spintria
Fludd Gallery: Melodic chair. Pale Mommet
Rowenarium: Rowenarium, use hush house key. Numen Book
Alter of the Knot. use Hill and Hollow or Tridesma Hiera. Numen book
Shrine: the Chancel: use sickle & eclipse or sacra limiae. Numen book
Shrine to st Tentreto: Alter: st Tentreto: use preliminary meter or Resurgences and Emergences and ink. Numen book
Oubliette Confinement. Use discipline of hammer or discipline of scar. Numen book
Librarian’s quarters: take inscribed stone and use it in any bed with edicts inviolable or edicts liminal. Numen book

You may already be aware of this one. Take the 18 busts of previous heads of the house and place them in the proper order in their slots on the grand staircase. Curate the statues and you will get a free soul card.

This part requires the House of Light DLC. Found a couple of interesting events that can happen in salons. Haven't fully explored things yet though, so this part will be particularly incomplete. Certain characters will have followup stories, and certain things can lead to unique text (like giving a character a certain food).

Arun and Denzel have a potential fling.
Zachary Wakefield has emotional response to onion gratin.
Princess Coquelle wants an introduction to one of Azita's friends.
Corso is interested in Mr. Kille's poetry
Stanislav asked Douglas to look into the death of Abbess Nonna
Mrs. Kille has an emotional response to Domaine Ravaline
Arun and Coquille have a familial connection
Connie and Agdistis have a shared interest in Oranoscopy
Olympe and Mr. Kille have a shared interest in music
Reverend Timothy has read one of Arun's books

And finally, a little fun thing if you play a lot. On the stairs in the "13th Librarian" slot, place any object. In your next game after completing your current one, that object will appear in the "12th Librarian" slot. Useful for getting an extra of a valuable object on a followup game.

This guide is by no means a complete one. I am certain there is much more to find. If you know of anything, I may add it to the list.