This is the bonus cache for the Adventure Lab cache 'Welford Road Cemetery' (see https://adventurelab.page.link/QTmk).
The physical container is not in the cemetery, but you will need to visit the cemetery and complete the Adventure Lab which will tell you the final coordinates for this cache.
The cache is accessible fro outside the cemetery at all times, but during the day, when the cemetry is open and there are lots of people around, it will be more easily found from inside,