Here is the full list of all 58 Horace achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete all other achievements.
Complete the game.
Reach the end of the game having cleaned one million things.
Find all the secret rooms in the mansion.
Read 15 teletext pages.
Clean 1000000 things.
Find all the alternate title screen skins.
Complete the auto map by visiting every room in the mansion.
Die 1000 times.
Push all the rubber ducks into the water in the Laundry Room.
Save the Man in Black.
Don't save the Man in Black.
Win The One Tournament.
Defeat the helicopter boss.
Travel to the secret moon base.
Defeat the Ether boss.
Defeat the Fire boss.
Defeat the Air boss.
Defeat the Water boss.
Find an alternate title screen skin.
Buy all possible shop items..
Find a secret room in the mansion.
Defeat the Earth boss.
Reunite with Heather and the Old Lady.
Meet up with Alice and Sim.
Kidnap Mr Deck from the TV Studio.
Get the high score on all the arcade games.
Get the kids blamed for shop lifting.
Watch a train arrive and leave at any station.
Go on a most excellent adventure with the Professor.
Catch 200 objects.
Run the BASIC program everybody knows and loves...
Clean 100000 things.
Take your first train ride.
Earn £10000 from jobs, junk yards and other winnings.
Help to sort the post.
Help to make bricks.
Buy an item from a shop.
Play an arcade game.
Earn £1000 from jobs, junk yards and other winnings.
Earn £100 from jobs, junk yards and other winnings.
Help to wash dishes.
Spring Logan from prison.
Learn to play the drums.
Empty 10 bins.
Defeat the Nanobot Boss.
Defeat the K-Bot 100 Boss.
Score 100 baskets in total.
Use the Atlas Gloves to tidy up the village hall.
Of dead Old Men?
Return the blind man's cat.
Rescue the family from the burning house.
Clean 10000 things.
Venture out of the mansion.
Climb walls with the Shoees for the first time.
Clean 1000 things.
Clean up your first thing.
Completed basic robot training.