These are some hints for SOME of the hidden locations

Cannabis Processing 

 

 

 

Black Market

 

 

The beginning of money laundering

(Money laundry for newbies) 

 

 

The Haunted House 

(Find all the objects to get inside of the haunted house. You will need a book and a set of keys which both are spawned in random places around the house, the illegal cooking bench is located inside of the haunted house, Have fun!) 

Speak to Jeremy and follow the clues to get the objects to get access to the haunted house. This can only be done in-game night time.