Let's see.
I wouldn't make it that obviously scary from the outside.
It would be a gigantic church like building with a massive tower from the outside, with gothic architecture. It should be beautiful, but also give off an aura of ominous ness.
Something much like the church of Notre-Dame de Reims actually, but much bigger and taller.
Although he is rectulant at first, Link manages to convince a girl from the village to accompany him.
Once Link and the girl enter, they should be greeted with a massive room. Beautiful yet a slight tinge of something wrong.
There is a shine to the goddesses at the end of the giant room. As Link walks down the halls, he notices less and less light coming from the windows. Right as he gets up to the statue of the goddesses, it seems to have somehow become completely nighttime, and all of the candles have lighten themselves.
As he looks over the statue, suddenly all of the windows shatter. A massive crack forms in the middle of the room, and much screaming from voices unknown is heard. Link then notices that the girl is on the other side of the crack splitting the church in two! The crack develops into a massive hole, and although they both try to avoid it, suddenly a massive beast smashes through the door which they entered. The girl begins to rush away from it, but she then trips and falls into the hole.
Before Link can fully see all of the monsters, the floor caves out from him and he also falls into the hole.
He is awoken in a strange room. There are many levers and switches, as well as a massive block puzzle. A small sign is in front of him
"Trapped, are you? It's not...so bad. You'll get used to it after a few...centuries."
Link must solve the puzzle, something which is hard. When it is solved, the ceiling suddenly sprouts spikes and begins descending. Nothing can be done. Link crouches and crouches, but the spikes descend and kill him. The Game Over scream appears and you are taken back to the menu.
Link awakens in what else but his house! His friends are there and so is the girl. They explain that he ran into the church, and about an hour later came running out screaming and passed out. He had injuries, but they are healing now. As Link begans to wake up, he looks out the window and notices that the sky is jet black.
At which point when Link turns back to his friends, they are mutating into hideous monsters. Link grabs his equipment and runs out of the house into the unknown. Monsters grab at him as he runs through the world with a jet black sky, that looks somewhat like his home town but not quite.
He sees an interesting building he has never seen before. It is gigantic. He runs into it, and falls down 20 feet when he opens the door. The door was on the ceiling...
At which point the temple will pay many mind tricks on you.
There will be one very disturbing scene right before the boss battle where Link walks through a door into a bright sunny field. His friends, his little brother and his deceased mother will be there. They are excited and happy to see Link.
Link however then notices a cage. The girl that helped him get into the cathedral is in it! She is screaming for Link to help her. She is chained, and being whipped by two floating fire whips, something which looks quite painful.
A small monster then appears. Link tries to dodge and kill it, but it lodges itself onto his arm, and crawls under his skin, causing horrible pain.
The field turns into a small brick room, with the walls covered and blood, this room looks much like many others in the dungeon.
Link's little brother, deceased mother and three friends start beckoning him to commit suicide. They claim that he can finally "Be with them" and he'll be happy. The demon in his arm is causing him awful pain now. The friends are telling him it will stop his pain, and his dead mother says that he can be with her forever if he commits suicide.
The girl begs Link to attack his family and friends. She says they are demons in disguise, and they cannot escape and the pain will not stop until they are killed. But when Link gets close, they seem to be acting just like his family and friends. They begin to cry and beg him not to hurt them.
If Link talks to his friends and family, they will ask him to commit suicide. If you say yes, Link will plunge his sword into his chest and the game over screen will appear. The game intro screen and select a file will appear, except the intro is just a black screen with disturbing music and the game logo. You may then select the file. A horrifying demon appears and begins to laugh.
"So you fell for it? You really thought they were your...family? Hahah! You may come to think of me as...family. We'll be together for...eternity...." and the game over screen appear again. If you select to continue, you'll be right back at the entrance of the dungeon, with all of your progress lost.
If you don't commit suicide, you eventually have to start attacking your family and friends. They plead for you to stop, talking about the horrible pain and asking him how he could do this to him. Eventually if Link attacks them through the horrible screams enough, they will be revealed as five demons. You must then defeat them, and then Link and the girl are free. You get the Big Key and appear in front of the Boss door...it is time to fight the boss.
But yeah, generally a horrifying and disorientating dungeon.