As a resident of Bolinbrook I can add a few other items of interest possibly.
My family has resided in the village since the Domesday Book, descended from Sir Robert Skynere a Norman born as it says on the Church records.He married the daughter of Sir Robert Bolingbroke of Bolingbroke. The title 'Sir' disappears with the ninth descendant Richard, but they continued to marry into titled families for many generations, Richard himself married the daughter of one Sir George Lambert although I can't decipher exactly where the Lamberts hailed from.My family seem to be the ancestors of the Skinner family in many other counties judging by the records, whether all Skinners can be traced back to Bolingbroke I cannot say for sure.
You will find stone from the castle used in a row of workmens cottages known as 'The Row' up near the Hall.
The Hall was once the residence of William Stones, a well known Victorian water diviner.
With the sandstone of the castle being a relatively soft material it is easily carved, as you can see from the unfortunate amount of graffiti left by other previous visitors. It also lends itself to fossils though, and when I was a youngster I found a large piece, from memory roughly 10 inches long, on the floor of one of the gatehouses with the fossil of a brooch in it which clearly showed the three plumes of the emblem of the Prince of Wales. Unfortunately, I took it to school and my teacher took a fancy to it and I never saw it again.
On my hearth I have a cannonball from the ECW which was one of a pair dug up by my grandparents at the bottom of their front garden along Hagnaby Rd which runs adjacent to the castle along its Western side. These balls weighed 5lbs and approx 9 lbs respectively, both of cast iron with a seam around the middle.. My late father used then as door stops in his office for many years. Unfortunately a secretary took a shine to the larger one and when she left his employment it disappeared at the same time.
If you look at the aerial photo Hagnaby Road runs along the top of the picture. There is a triangle of trees top right with another clump to their left next to the road. Above them are two bungalows on the left of a road leading into a housing estate. Cromwell House is to the left of these bungalows, set back from the road with a large front garden. The cannon balls were found whilst digging a fishpond at the bottom of the garden near the road. That gives you a rough idea of the distance. The question is, were they left there by the Parliamentarian besiegers, or were they fired out from the castle itself? I prefer to think that they were fired at the Parliamentarians, and possibly buried themselves in the soft earth, it being October when the siege took place.
The field to the South of the Castle is known as the Rout Yard. With it having raised banks of earth all the way round there has been speculation as to whether it was a large cattle pen, and the earthwork in the centre some kind of fishpond. However, during the visit by the Sealed Knot when the seige was re-enacted it was used as a defensive earthwork to disrupt and break up Parliamentarian attacks. This seemed to be the latest thinking on the subject. It wasn't dug to protect the attackers, but rather to protect the castle at a reasonable distance and deny that part of the field to the enemy.
The castle was dug out by the council in the 60s and they had a small team working on it full time rebuilding parts and digging other bits out. It all seemed to stop when the stone mason had a heart attack and died, although that might have been coincidence. I recall Cambridge University used to come for a week every summer in those days and do a dig, always in the same place though where the Kitchen midden had been. Apart from recently digging the moat out as it was badly silted up the castle has been largely left undisturbed ever since. I know that my former history master who lives next to the castle used to own a sword which was reovered from the moat, but that it the only other artefact I am aware of.
During the siege the Parliamentarians put a gun on top of the church tower so they could fire down into the castle. The church used to be twice the size it is now, I think it too was damaged after the Civil War finished.
A former girlfriend of mine ran the village pub a few years ago, and caught her son who was aged about five at the time, talking to someone in his bedroom. However there was no one to be seen. When she asked him to describe the man he described a soldier of the ECW. Several days later he was also overheard talking to someone in the rear courtyard.When asked who it was he said it was the same soldier, however he looked different this time. He described how his hair had all been cut off at the back of his head. We were told that there was a courthouse on that site previously and having the head shaved like that was the sign of a condemmed man.
Coincidentally, my chldhood home was also a former pub, the Duke of York, besides being the village brewery, home to Castle Beers. It too was haunted, by the ghost of a scullery maid in our case.My great grandfather lived there until he passed away from pneumonia, caught by him trying to swim the moat one November night on his way back from the pub absolutely steaming drunk.
The castle is also supposed to be haunted, by the ghost of a white rabbit. I've never seen it personally, although I thought I did one night when on my way home absolutely steaming from the pub I passed the castle and the thought of the ghost of the white rabbit had just entered my mind when I met someone in the pitch black darkness of Moat Lane, and they were wearing white trousers.Frit me to de'ed as we says around 'ere.
The site is supported by a local friends group as you say, although some residents prefer to refer to them as the 'Fiends', with their tongues only slightly in their cheeks.