This cache is part of a series of seven caches placed at or near wells in the Chilterns. At the top of the logs (of six of the seven caches), you will find a number - eg A=1, B=2 - which you can use to get the co-ordinates of a bonus cache.
You can park very close to all the wells, so most of the caches can be done as drive-bys. If you want to do them as a circuit, you may want to do them in roughly numerical order - starting at Binfield Heath, then Rotherfield Peppard, Gallowstree Common, Kidmore End, Ipsden, Stoke Row, Highmoor and then the bonus...
Some geology/history... Chalk is a very porous rock so a high percentage of rainwater just seeps through the cracks and fissuresin the chalk down to the water table, rather than collecting in streams and rivers. In previous centuries, villages up in the Chilterns often suffered from severe water shortages and relied on wells for their water supply - many communities didn't get piped water until the mid-1900s. Maharajah's Well in Stoke Row is almost certainly the best known well in the area, but there are many more, both beside roads and also in people's back gardens. Most of these wells date from the mid to late 19th century.
Gallowstree Common The well is 300 feet deep and is shown on an 1873 Ordnance Survey map, so was obviously built some time before then! The wellhouse is a listed building. It has low brick and flint walls on three sides - the fourth side being open for access to the well.
You are looking for a small plastic container. Please be ultra discreet - there are houses nearby