Through some sleuth Googling, I did find this (although I'm kinda wishing I hadn't! :P). I found it by searching for "fanfiction harry potter 'safehaven' password", where it is the second result (this question is the first).
The story is called Strengthening Wounds, and is written by user Louis IX on FanFiction.net.
It started with Harry living with the Dursleys. Vernon and Dudley were abusing him (I remember him being stabbed with a fork) and they beat him to death, I'm pretty sure.
"Come on... sonny! Let's give... the freak... a last run-down." The
underlying tone was clear, and frightened Petunia Dursley. [...]
"...do you think I can touch the heart with a fork? Ah, missed, bad
luck..." [...] It was a long time until both Dursley males turn back
into the living room, a demented gleam in their eyes, and blood on
their clothes and hands." - Chapter 6, Global Destruction
Then I think the house caught fire and burned down around Harry's body
and the Dursleys all died? Harry woke up without any memories.
"As soon as the lid opened, the liquid fire engulfed the corridor,
setting fire to everything." - Chapter 6, Global Destruction
"He sensed something on his right hand, and looked down. A signet ring
with "G/S" on it. That sealed it, he was convinced now. His name was
Gabriel Swift. What little was left of Harry Potter left the shoddy
area towards the city, and a new life." - Chapter 7, Mourning and the
The story gets fuzzy in my mind here (I think I was 12-13 when I read this, so around 8 years ago)
The fic was posted in 2005, ten years ago. (FYI, it's rated M - 16+ unverified, with content suitable for mature teens and older.)
but Harry had secret rooms. I think he had a ring or a necklace or something that held the rooms, in a way. They could only be opened with a password, which he set to be 'safehaven.'
"His heart beating at his discovery, he braced himself, and, still
holding the book, spoke aloud. 'Safehaven.'" - Chapter 14, Surprise,
"He found himself on a bed, panting. His heart beating fearfully, he
rose and started to explore his surroundings. It was quick, because
the place was small. Small, and without any door or window. He started
to panic, and scanned the set of rooms rapidly." - Chapter 15, Room
I know at one point, he meets up with Ginny and they go into his rooms and I'm pretty sure that is left to the imagination.
I'll leave you to find that passage, I think.
I remember the author's name was a man's name with Roman numerals at the end.