It's a long lived fortress on a small world, optimised (i use a 2x2 fortress map for this one) for keeping high framerate so quantum stockpiles and atom smasher helps to keep things in control. The fort provide enough happy thought things and other tricks to keep depression to a very minimum (depressed dwarves have always been dealt with by sending them to some distant hillock anyways)
At the time of the save there's 72 dwarves ruled by a countess, most of them are also in the military.
There used to be more but there was a price to pay for multiple wars against gobs.
Anyways the adamantine can be found by pressing F6 (custom hotkey i set to my fort main point of interest)
The tunnel from the surface exit right in front of it.
The entrance to the tunnel leading directly to the adamantite is on the exterior of my fort, so it's possible to keep the dwarves out of the demon fun party.
At the time of my save i enabled the alert, so the civilians are confined into the burrow (that is the safe fortress grounds).
To disable the alert (so you can at least send a miner to do the final digging deed) just press
m -> a -> then press enter to set the alert to Inactive.
If you want to save your dwarves after doing the deed and re-enabling the alert, you can also lock the fortress by raising the entrance bridge to block the fortress entrance by using this lever in the Countess halls :
there's another lever at some distance , it's for controlling the atom smasher, no need for it.
the fortress was made in df44.12, no dfhack or any mod used (so none needed to play), i use only this simple custom tileset so you can use plain ascii or your favorite one :