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