Glyn
I am going over in June, 11th to 17th, basing myself at St Pol, looking at a 2 day hit of some sites. I want to do the Wellington Quarries and the Last Post. Is there a crater site or some trenches handy,
Nigel
If you only have two days, I'd suggest narrowing your scope a bit.
Wellington Quarry is in Arras and Arras is good for Vimy Ridge and the Canadian Memorial where you will find restored trenches (but a bit antiseptic).
You will also be close enough to do some of the Somme sites, such as Lochnagar Crater, Thiepval and Newfoundland Park near Beaumont Hamel (much better, unrestored trenches but not as good as some to be found near Delville Wood).
Alternatively, Fromelles is in French Flanders, not too far from Ypres and it's Ypres you will need to visit to witness the Last Post.
Not far from Fromelles is Neuve Chapelle and Aubers Ridge (two significant battles of 1915) but they are not easy to unravel today without a lot of maps and quite detailed research.
Ypres is good for lots of mine craters from the 1917 battle for Messines, Tynecot cemetery and a small but interesting trench preservation called Yorkshire Trench in the north of what was the Ypres Salient.
In Ypres itself is the excellent In Flanders Field exhibition in the Old Cloth Hall.