Here is the full list of all 55 HROT achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Achieve a score of 200 points on a handheld game
Find Tuzex vouchers
Complete 6 different levels on Very High Difficulty
Locate the secret level
Find a postcard from the creators of Project Warlock 2
Surprise the newt in the cabin
Kill a monster by knocking it off somewhere high with the footkick
Gottwald's body missing
Discover a secret of Vyšehrad Castle
Kill 5 monsters with a sickle in a row without damage
Check the simulator
Get past wave 15 in Endless Mode
Get past wave 10 in Endless Mode
Survive wave 5 in Endless Mode
Complete all three episodes
Complete episode 3
Give a gastroscopy
Hit an enemy with the soccer ball
Get through a level without damage
Shoot down a flying pigeon
Free 4 Ratters
Pet two dogs
Waste three minutes watching the model railway
Hit the enemy with a kicked grenade
Early Access sauna is a cold place
Have a gastroscopy
I really like this random stuff
Kill 35 monster types
Complete episode 2
Clean all mess after the Degustation
Find all plates in the Granny's Valley and bring them to the Degustation
A lot of wine
Anger the bees and run away
Kill Headsman in air during jump
Find 50 different secrets
Start the mining train
Complete episode 1
Burn 4 monsters with one bottle
Gib a horse
Kill or damage 10 monsters with landmines
Kill 500 monsters in total
Find all secrets in a level
Find a second pistol
Run over 10 monsters
Kill all monsters in a level