He'd mislaid the number and so rang Directory Enquiries. "Can I have the number for Conisbrough Castle?" he asked. I imagine he had a reedy tenor voice but that's just me trying to fill out the story, in my version of which the Enquiries woman sounds like Thora Hird. "Nobody lives there, love." she replied. "It's a ruin!"

I thought about that tale the other Sunday when we took our grandson, Thomas, to the castle to, in the time-honoured Yorkshire phrase, "pass a bit of time on".

When our own kids were little, Conisbrough Castle was on the trail for the empty Sunday afternoon or the quiet weekday in the holidays.

It was a well-worn trail, that one; a compass with loads of points: Conisbrough Castle, Worsbrough Mill, The Yorkshire Sculpture Park, Elsecar Heritage Centre, Brodsworth Hall, Cusworth Hall, Monk Bretton Priory and Roche Abbey, all preserved to this day in boxes of old pencils and notebooks bought from gift shops and photos in albums and memories held in the mind.

I guess that my family, born in the 1980s, were the first generation to experience the idea of "heritage", the idea that places like South Yorkshire could re-invent themselves after the decline of heavy industry by becoming sites (to use a heritage word) that people might want to visit for a day out or a weekend break.

I guess the high (and low) point of those times was The Earth Centre, sited on the old pit at Cadeby, and a dream of one man that never quite fulfilled its promise.

When it first opened, many years ago, we went to have a look, and a lad with dreadlocks pointed us towards "the miners' trail" which looked to me like the path that my father-in-law walked down to Houghton Main. Heritage and real life seemed to be clashing together a little, so we cut our losses in the slight drizzle and went to the tea shop.

The Earth Centre brings us back to Conisbrough, of course, and we drove with Thomas past the shut-down site on the way to the castle. In Denaby, we passed the place where the library used to be, where I ran a writing workshop on a Monday night, and suddenly I had a pang of nostalgia and felt like a bit of heritage myself, a man who seems to live his life and take all his moral and political and cultural decisions through the prism of the 1980s. Nobody lives here: I'm a ruin.

So we trundled up to the castle and went to pay. Thomas was excited by the idea of the castle because he likes what he calls Knights in Shining Armour (the armour always has to be shining, and quite right too!) and at our house he's got a helmet with a visor that my wife made out of cardboard.

He always points out to me that a helmet always has to have a visor, just like a car has to have a spoiler. He's a lad for detail, our Thomas, which will probably stand him in good stead as the 21st century zooms along.

As we stood to pay, though, something else caught his eye: a toy helmet with a visor and a big red feather. He was drawn to it like a Barnsley fan is drawn to FA Cup glory.

In a grandparentish way, we said he might be able to get it once we'd looked round the castle; that's always how the sequence should be, isn't it? Educational visit first, tea shop after, gift shop last of all.

So we went round the castle but I could tell that his heart wasn't really in it: his heart was in the shop, in the helmet, in the visor.

So we went back after a while and he picked up the helmet and tried it on; the visor clicked down and I could tell he was in love.

Of course, there was no price on it, and, of course, when the bloke in the shop checked the price it made my hair stand on end but, hey, what are grandparents for if they can't be a little bit indulgent?

So we broke the rule and went visit, shop, tea shop. Thomas sat in the tea shop with the helmet on and the visor down, like The Man in the Iron Mask on a day out. He leaned over his toasted teacake and his plume went in my cup of tea.

So that's why his feather's a little bedraggled; just like a real Knight in Shining Armour after a long day's jousting.