There is a concentration of 14 pillars around Fort Augustus called the Great Glen Project that were used to measure crustal movement across the GG fault and not for OS mapping ( as such they do not show up on the OS map but they do count towards the final TP tally). 15 are recorded; one has never been found, probably never built and another one was only found this year. These are a very do-able "round". Even more acheivable ( although access can be problematic) are the 9 Curry Stools, 6 of which are in Scotland. These are not the result of an excess of chilli but you do need to visit a bog to find them.
http://trigpointing.uk/trigs/view-trigs.php?q=1774092There is an interesting article from Rob Woodall on the OS website written shortly before he reached his final TP. I wonder how Dave Hewitt has got on with visiting pillars at all the different heights
https://www.ordnancesurvey.co.uk/newsroom/blog/britains-top-trig-baggerIf benchnarks, bolts, rivets and other types of triangulation stations are added into the to the tally the number leaps to over 25,000. I only record the pillars and only started doing this a few years ago when I came across the TUK site ( although added retrospective ones from the hills I had recorded as having climbed). My 395 tally looks somewhat pathetic.