This cache is placed at a bridge of the Midland Mainline railway. Originally another railway line ran by here before the current railway line was built. The original line was part of the London and North Western Railway (LNWR) between Rugby and Peterborough that opened in 1850. This was the first railway line to reach Market Harborough. Due to the Grouping Act the line became part of the London, Midland and Scottish Railway (LMS) in 1923, then later British Railways, before it closed in 1966 as part of Beeching's cuts.
You may have noticed that the main road near to the cache location (in a northerly direction) goes up over a bridge, this was originally over the old railway. If you walk under the railway bridge at GZ and look to your right you will be able to see where the line passed under the current railway, if you look to the left you will see the current railway access road which was where the old line was. It must have been quite a sight back then with these two lines running side by side and then crossing each other.