Long lost Railways around Wigan
This cache is situated in a very quiet area of Standish,
a long forgotten bit of land, it's actually a disused railway
line, now nearly reclaimed by nature, the bridge/short
underpass here is still an original feature though, trains
used to run under here when avoiding Wigan, mainly freight, but
occasionally passenger trains when the need arose, nowadays they
just pass over the top, no doubt you will see a few when finding
this cache as it's very busy.
The Lancashire Union Railway
The LUR also built a line, the "Whelley Loop", that bypassed
Wigan to the east. It opened in 1869, mainly for freightStations at
Whelley and Amberswood were open for only three months
between 1 January and 1 March 1872 Additional connections were made
to the NUR's West Coat Main Line north and south of Wigan in
1882 and 1886 respectively, and to other lines radiating from
Wigan, thus allowing many trains to bypass Wigan.
The old lines -Below is a map of how Wigans' lines in
this area used to look:

The loop line is long gone, I've marked it with an arrow where
this bit of it starts and finishes on the map, if you look further
back this is where the 20 Arches viaduct is situated (see below),
the line eventually joins back on at Springs Branch, in Ince..
Further along the line there is a great viaduct, now mostly
hidden, it was known as 20 Arches, it's still
there and really worth seeing although tucked away it can still be
reached even in a car.. More info can be found here on
Wiggineers cache page, yes,
there's a cache there too, and it comes highly reccomended, here it
is:
GC1QW2J TWENTY BRIDGES
20 Arches viaduct in 1970:

The cache you are looking for is small container that will
easily take small TB's and any coins, hope you enjoy your visit,
you can see how times have changed from the days of old ! - at the
times of placing the signal was not superb, I think it should
definately be within 20 ft though, with the clue will not be a
problem although it is well hidden