The starting coordinates should bring you to the pavement near to the entrance to the ladies toilets. For men, take a walk up the ramp between the ladies entrance and the exit from the car park and you will spot your entrance. Between the two entrances you should see the PT number. If it is missing then enter your appropriate door and you should see a copy inside.
I checked out the women's. The interior is bright and welcoming, apart from a slight mal odour. Of course that might be because it may have been a while since they were last cleaned.
The lower two thirds of the walls were covered in bright white tiles apart from a vertical strip of bright red tiles opposite the entrance. These red ones certainly added some colour to the facilities. On the wall to the left you had a stainless steel hand basin with a liquid soap dispenser above, and a hot air hand drier to the side. No mirror is present.
Two cubicles divided by stainless steel walls that have a gap before the floor and don't reach the ceiling are opposite the handbasin facilities. The cubicle doors are also stainless steel and are locked by turning a handle to slide the bolt. The toilet bowls are stainless steel and jut out from the wall. The cistern is behind the wall and a stainless steel button for flushing is on the wall above the toilet bowl.
The wheel chair accessible cubicle has hand rails to provide extra assistance. Both cubiles have a sanitary disposal unit and a toilet paper holder that can hold two large rolls.
I assume that the men's will have a urinal or two replacing one of the toilet bowls and will have everything else that is generally expected.
I would assume that these facilities are locked at night, hence their tidy appearance. If you are caught short then continue down and around Moray Place, crossing Princess St and Lower Stuart St to the 24/7 facilites at the bus hub in Great King St, opposite the entrance to the supermarket.
The cache is located at S45 5A.BCD E170 2E.FGH
A = On the outside of the door leading to your appropriate choice for usage you will see a sign with a wheelchair symbol on it that is screwed to the door. Count the number of screws used to fix it sign to the door.
B = Go to the nearest parking metre to the given coordinates. (It should be located on the edge of the footpath just down from the facilities). Use the first digit of its number.
C = Sum of the PT digits
D = First digit of the PT number
E = Numer of screws holding the door handle to the door plus the digital sum of the parking metre number
F = What is the first digit for the parking time (red label on parking metre)
G = Number of attachment points of the ramp handrail to the wall, minus the sum of the second and fourth digits of the parking metre number.
H = Use the digital sum of the address.
Check Sum = 40
From here it is quite an uphill grunt to the cache if you chose to walk. Parking is available in the GZ area and the toilets themselves are located by the vehicle entrance/exit to a parking building. You might be lucky and get some onstreet parking but be aware that Moray Place gives the city a healthy return on parking fines.