I'm sure this has been found before, but it is new to me.  When I try
to fly the helicopter into the building across from the Malibu it
always seems to catch fire.
There is a walkway just south of the North Point Mall.  This is near
the police bribe, parked car and Adrenaline pill.  There is a railed
walkway just next to a nondescript building.  If you pan the camera as
you walk down the walk way you can see into the building/underworld.
If you park a car in the walkway you can jump up onto it and into the
underworld.  After a few seconds you end up back in the game.  I also
just noticed that if you stand next to the rack of monitors near the
bank guard you shoot in The (bank) Job, you can scan through the
monitors.  Now where did you put that disk?