Is there any secret cars in Grand Theft Auto 4?

Answer 1

There is a car secretly tucked away out of sight in GTA IV, and this is a Sultan RS. This vehicle can be found well hidden behind the old garages/sheds in the grounds of the ruined mansion in Westdyke, Alderney. This is the old mansion that Niko drives the hijacked van full of coke to for Phil Bell. It is in the north of Alderney and the track leading to the old house is just over the road from the Burger Shot there.

Answer 2

If Niko acquire's the apartment belonging to Playboy X, by making the appropriate choice in The Holland Play, he will find Claude's outfit from GTA III in the wardrobe.