We had a nice stroll with our friend Gilles around this little town, taking in a traditional toy store (where we bought a puzzle hedgehog) and the artists' house (where we met Dr. Price and Britain's longest-living lady). We met a nice lady on the castle green who showed us an intriguing grave in the churchyard marked "Not to be reopened". A plague victim, perhaps? It can be found at N 51°32.505' W 003°22.604'.
We found the cache after a few minutes of searching, then we sat on the nearby bench to sign the log.
Thanks for taking us around Llantrisant!