The O'Neils Farm is a farm house. In the mission Crystal Maze, after they steal a drug contract from Trevor, Trevor kills all of them except for four. He then burns down the house with gas in the basement. He then shoots the house and drives away on an ATV. The house eventually burns down completely.
The farm being burned by Trevor.
After the mission
When you go back to the house, it is completely burnt down. You can walk around the remains of the house, excluding the basement. There is a random event near by with a cop chasing a suspect so you can't shoot. The O'Neils ghost may be there,Haunting the house.Also Strange noises and screams are rumored to be heard there.