Two of my rarest: Dune Awakening

Dispatch

My overall showcase

And probably my proudest accomplishment

Video game news oriented community. No NanoUFO is not a bot :)
Posts.
Comments.
My goal is just to have a community where people can go and see what new game news is out for the day and comment on it.
Other communities:
Two of my rarest: Dune Awakening

Dispatch

My overall showcase

And probably my proudest accomplishment

How do you check again how many copies a game sold?
Because I have some 1% achievements in games that sold millions, but I'd argue my "20% of players" achievement in a 200 reviews game is rarer.
My sibling, why would you ever play witch it on an official server?
I have all the achievements for Final Fantasy 1
Not counting rare ones that are from brand new DLC, this is my rarest (Stellaris).

With another rare from a different space 4x game (Endless Space 2):

Edit to add the one I am the most happy with (Noita):

Is there an easy way to find out without using third party websites?
In your steam profile settings there's a tab named Showcase Manager in which you can choose to display the Rarest Achievement Showcase on your profile page, it will show your rarest achievements on your profile
Mine is nothing special. It's Architect of Ruin from Shotgun King. You get it for doing some minor progress in the new-ish (not really anymore, but it used to be new) Charnier mode, nothing challenging at all, but I assume the reason only 0.6% of players have it is because everyone moved on from the game before that content dropped.
Even silksong came out I got the achievement for fourth chorus when it had a 1% completion rate
I've got quite a few <0.1% from Lost Ark, but it doesn't feel like they count since it's a free to play MMO, so the account numbers are bloated.
After that I have a 1.8% from Forza Horizon 4 (30 stars on Skill Streak) and Frostpunk (Build the generator in the DLC mission).
Some test achievement for a game I was developing, to check that the achievement integration and unlocking worked as expected. It later got replaced by the real achievements, but my Steam rarest achievement showcase still shows it, so I’m happy to keep it for the lols. Probably only me and a couple QA folks could possibly have it. Well and cheaters of course.
All my latest most rare achievements are all from Megabonk, which IMO don't really count. They are easy to get if you just play long enough.
My rarest for a very long time was this one with something like 0.3%, but it has apparently since gone way up. It used to have one of those gold borders around it indicating it was very rare. I got this on my second round that I played and then quit pretty much right after that. Not a very good game, unfortunately.

The one I am most proud of is this one:

I got bored after I took over Britannia as the Britons and had no more enemies who could realistically challenge me, so I sailed directly down to Rome with my army of slingers and tribesmen and sacked Rome for something like 100k denarii.
EDIT: Well, nevermind, this is my newest rare achievement (for now)

One of the rarest achievements I have is not at all difficult. It's not even trying to be. It's on Street Fighter 5 for saving 30 replays. Apparently nobody does that?

This one is the rarest of the game

This one is less rare but actually more difficult. Far more people attempt it so it has a higher achievement rate.

This is my rarest but it's a small part that nobody plays of a niche game.
0.2% - American Truck Simulator
Shining Star
Obtain 3 stars in any 3 scenarios played in a row in Truck Driving Proficiency (Driving Academy)
The one I'm proud of:
0.3% - Halo: Master Chief Collection
A Preference for Pain
Halo 3: Complete the Halo 3 LASO Campaign playlist.
My top 20 rarest achievements according to steamvault were all dirt rally ones about beating easy stage times...
Not many people played dirt too seriously it seems 😄