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