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