Small cache hidden on the 2°W line of longitude on the newly created River Rea Trail.
The line of longitude, 2°W, is the only line of longitude that coincides exactly with one of the lines of the Ordnance Survey National Grid. It's line 400000 of the National Grid, also known as the Central Meridian, for those who like to know these things. It also runs the entire length of England: from just outside Berwick-upon-Tweed on the north-east coast to a couple of miles south-west of Swanage on the south coast - a total of 359 miles.
The author and television presenter, Nicholas Crane, whom you may have seen on BBC's 'Coast', once walked the whole line from north to south. He allowed himself a margin of just one grid square either side of the line. After the walk he wrote a very readable book called "Two Degrees West" which describes his escapades. The book is now out of print, but still available from second hand dealers.