It is also not an actual round-about, but it is round, as is the nearby virtual site!
If you complete the whole series you will have found every cache size, a most 'terretrial' types possible, and hopefully a few interesting caches too.
The YOSM is a Virtual Cache (GC45CC) that moves around Ye Olde Survey Monuments, but it can be logged from previous postings, and it was once close by! To claim it you will need to visit the trip-point on Hoon Mount; the waypoint below shows the site of the trig-point; Make a note of the OS number on the plaque then, when you log the cache, email that info to the CO to confirm your finding. Then, if you have done the whole RoundAbout Hilton Series you will have also found a Virtual Cache to add to the list of cache types. (YOSM Hoon Mount)
It is only about 3 miles out of the village, but there are some spaces to park along the lane close by, just be careful not to block the lane as it is in frequent use.