This is a physical cache, which you can find after completing the Pottering around Lacock Adventure Lab. There is nothing at the posted coordinates apart from limited free parking. There is also a much larger, but chargeable to non-members car park close by, just follow the NT parking signs.
You can find further details about the App for Adventure Labs here: https://labs.geocaching.com/ then simply check the app once in Lacock and you can start the trail.
The whole Adventure Lab and the bonus cache should take about an hour to complete and the route to the final will be muddy through the winter months.
The Little Bridges series was started by Stanthews in 2009 to highlight small footbridges in remote parts of Wiltshire. Since then the series has been expanded by others all over the country and starting to spread fast. There is a stats listing run by Billiethecat, so you can see how many Little Bridges you have found, you can view it here. If you would like to add to the series, please contact Stan (stanthews@aol.com) and he will give you a number for your bridge, to qualify, the bridge must be a foot bridge too small for vehicles, please make sure your title exactly matches “Little Bridges # xxxx then the name” including spaces so it will get picked up and added to stats list.