There is a glitch that seems to be virtually unknown / not heard of that makes getting this achievement very simple ... Many thanks to Vermintide player UnstumpablePepe who showed our group how it works .
So play thru the level ( Cursed Rune ) , ideally on easy but You can use which ever difficulty you like , until you reach the elevator . Once at the elevator clearout as many enemies from the top as You can ... Your Elf will ideally have true flight arrows which makes this fairly simple .
Once You are satisfied that You have cleared out as many as possible be aware You will still get sporadiccally attacked whilst hanging around at the top ... But this will not negate the achievement as the ' Event ' starts once You activate the elevator ). Activate the elevator - the event has now started - when it reaches the bottom take a second to ensure there are no enemies around ... If so kill them with ranged weapons.
You now need to make Your way ,as a group , to the left of the temple where the Rune is ... There is a track that you follow and as You follow it You will notice a large rock directly in front of You.
Once at the rock , You will notice that there is a small edge that You can start to walk round, to the left hand side of the rock ... at this point You need to slightly walk around this edge and then make yourself fall of it so that You are just hanging there ...
At this point another of Your group needs to pull You up and THIS IS WHERE THE MAGIC OCCURS .. As You are pulled up you will then be inside the rock. The next guy then falls of and is then 'rescued' and again He is inside the rock then do this with the 3rd guy ... This should leave just 1 person not in the rock .
This person , ideally equipped with a speed potion , goes and activates the temple door then makes his way back to the rock as quickly as possible ( hence the speed potion ) HE CAN STILL SUFFER DAMAGE AT THIS POINT IF ATTACKED which will negate the achievement.
As quickly as possible He then gets in the rock following the previous procedure ... Falling of the ledge and being pulled up !
If ALL has gone well you are now ALL inside the rock ...
Sorry, this Game Clip has been removed
Not our best effort ... But it shows the procedure - Scroll forwards to 42 secs to see the 'Getting in the rock ' procedure !
Whilst in the rock ... You will notice a sort of shadow /outline of where the rock is on the floor and you need to ensure that You are All standing towards the back of the shadow but within where the rock would be -If you are too close to the front You may suffer accidental damage again negating the achievement .
There should be very little movement whilst in the rock as You may accidentally push one of your team mates out of the protection that the rock offers .
You will notice that You can see out of the rock and at the same time USE your weapons to kill the enemies who congregate on the outside of the rock and even on top of it ...
Sorry, this Game Clip has been removed
We were running a Dwarf ,Soldier , Wizard and a Elf so we had the Soldier and Dwarf just stand there with shields up to offer some extra protection ,altho it wasn't really needed , whilst the other guys picked of the enemies . Make sure that the 'Specials' are taken out as soon as possible .
After around 5 minutes or so Your achievement will pop providing that there has been no team damage at all ... You can then just finish the level , if You wish , simply leave the rock by running out of it !
To summarise ..
1/ The Event starts as You activate the elevator.
2/ Head left of the Tomb along the track
3/ Edge around the left of the rock and fall of .. get rescued and now be in the rock .. Do this for 2 others
4/Last guy activates the tomb door and then quickly makes his way to the rock ( speed potion )
5/ Get the last guy in the rock
6/ Stand towards the back of the rock / Shadow on floor
7/ Shields up / very little movement / pick of specials ASAP
8/ Enjoy your achievement !!
We got this on our 3rd attempt due to a Gutter Runner appearing when the tomb door was activated and due to being to close to the forwards edge of the rock and thus taking accidental damage.
Again many thanks to UnstumpablePepe and to the rest of My group AnxiousAbe , Deathproof4289 & ArfurF00K5ak3 !
Any questions ... feel free to message me or ask in the comments !