The name of the cache was inspired by the famous LOTR scene where Gandalf stands on a narrow bridge and declares: "You Shall Not Pass". This new underpass is designed to help everyone to pass. When you are gathering the information, imagine Gandalf stationed in the under pass to welcome passers by, and to deal to any miscreants lurking in the area.
To work out the coordinates for this cache, you need to gather information from the underpass, and the city (eastern) and airport (western) ramps leading to / from it. There are three types of round thing on the ceiling of the underpass: lights, skylights and 'other' (might contain cameras). Examples of all three can be seen in the photo.
a = total number of concrete strips underfoot on the city and airport ramps
bc = number of ceiling lights in the underpass
de = number of skylights in the ceiling of the underpass
f = number of 'other' round things in the ceiling of the underpass
gh = number of panels on one side of the underpass
j = number of panels on one side of the city ramp
k = number of 'cyclesafe' drain covers in the underpass.
Note: each letter (a to k) has a 1 digit value. The checksum of a to k is 36.
The cache can be found at S 43 28.ABC E 172 33.DEF where:
A = h + e
B = b + d + g
C = j
D = f * g
E = a + c
F = f + k
Checksum of A to F is 39.
The cache is a round plastic container a short walk from GZ. Please push in firmly when replacing..
If you want to try another underpass multi next time you are up Nelson way, then have a go at Six (by) feet under SH6, which involves visiting 6 underpasses.