The directions and parking is in post #11 of this thread.
Procedure:
1 - You present your letter
2 - They give you a form to fill out (which will become your receipt at the end)
3 - They tell you to turn off your cellphone
4 - You fill out the form
5 - Someone invariably didn't turn off their cell phone, and the guards scream to have the phone turned off
6 - You drop the tray at the desk
7 - They call you in, inspect your passport and your hands, give you a card with a number
8 - You sit in the gray seats, and wait for your number
9 - They take your prints electronically, give you your receipt, and you exit by the back
10 - Take the closest door, make a left and you will be back at the parking lot