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