had mine last week, Friday
No need to wear anything special, T-shirt, pullover will do just fine. The only time when they will request that you undress is to check the lungs, heart function, reflexes, etc, physiological checks and obviously to see if you have to real arms. It was not required to remove the pants.
I went in at 8:30, at 12:00 I was already in the canteen, for a wonderful lunch.
Visitors parking has only 3 places right in front of the reception.
All process was very smoothly, everyone is very polite and helpful. It would help to fill in all the forms before your visit (even if on the form is written that you should fill in the personal data witnessed by their personnel).
Once the forms are with the reception and they identify you (passport, ID), someone will pick you up from the waiting room for the first set of tests. There were 3 rounds of tests, this is what I remember:
1. urine, blood, eye test 1, audiometry
2. lung function (capacity and speed), physiology exams
3. eye test 2, repeated lung function (machine needed calibration)
You receive the certificate immediately after.
I recommend the steak from the restaurant at the top floor.
Have fun.