A series of geocaches placed nearby to trigpoints.
The series can be added to by any geocacher by applying for a series number

What is Ye Ole Survey Monuments?

Ye Ole Survey Monuments, or YOSM for short (GC45CC) was a travelling virtual geocache placed on 25 March 2002 that was owned by outforthehunt. The cache moved around the country and you could be looking for a specific survey monument, pillar, surface block, rivet or bolt.

The cache moved around the country and as each location was a unique place; multiple logs were allowed. This was true until it was archived by Groundspeak in 2017 due to change in guidelines with a total of 25,076 finds by 3,528 different cachers.