It stands gleaming white, forbidding and stark, its towers staunch against an onlooker's gaze. Nearly 1,000 years of domination have not been softened under the onslaught of millions of tourists, tons of litter, endless cutesy shots of Aunty Mo with her head on the block. No, it's still the same: the architectural equivalent of a mailed fist knocking you senseless. It's the Tower of London.
If you want to understand what monarchy means, the role it has played in British history and the stark underpinnings of power, the Tower is the stones-and-mortar embodiment of that structure. From the Traitors' Gate to the Bloody Tower, the stories behind the walls are all of betrayal and death, loyalty and death, torture and death.
Although the the bulk of the weaponry once stored here has gone with the Royal Armouries to Leeds, there is still enough of the glittering materiel of war, the guns, shields and ceremonial tin suits, to remind you that the perception behind Chairman Mao's dictum "All power grows out of the barrel of a gun" was born long before the 20th century.
The genial Beefeaters love to make your flesh creep as they conduct their guided tours, but they are all retired soldiers, all men who know exactly what it means to serve Queen and Country, and not just by stroking the feather of a few old ravens. The big cannons on which the kids perch to eat their lunch have dealt not a little death in their time; the fascinating jewels of the crowns have caused much bloodshed.
Whether school groups focus on the exploration of the tragic histories of those such as Anne Boleyn and Sir Walter Ralegh, or an examination of the engineering triumphs of the moat and walls, there is much more than can be encompassed in a single visit.
On most days there is a choice of tours, talks and enactments. It is really thrilling to see, for example, actors dressed in Tudor costume playing the part of the City crowd which took Anne Boleyn's part when she was accused of treason. Here, vividly, children can understand that history is not monolithic, that events do not happen as in the history textbooks, sequentially, without question, but that at every moment real living people had everything to play for. They realise that Anne may or may not have had lovers but that she was a learned woman on whom the hopes of reforming Protestants were riding. That Henry was not only a jealous husband who wanted a dynastic heir but also a monarch greedy for absolute power, who was not about to surrender the spoils of his wrench from Rome into the hands of ambitious nobility.
All this can be so quickly conveyed by actors arguing on the cobblestones before the governor's house. Likewise, standing before the White Tower, we learn how Anne Boleyn had requested a French swordsman for her execution, who would accurately decapitate her with one blow. And as his modern counterpart swishes the air with his blade, the real horror of those mornings are suddenly brought to life. Imagine, those bound victims as they came to the execution block to be killed. Men such as Thomas Seymour, Queen Catherine Parr's lover, who only died after after several hacking blows of a blunted axe. It is a grim reality.
There are many static exhibitions as well as the crown jewels and armouries. The White Tower, first palace of the conquering Norman Kings, is now, together with other buildings of the medieval palace, fitted out in the styles of different periods, none of them comfortable but all of them magnificent. The Bloody Tower, which housed the wretched nephews of Richard III before their uncertain, but no doubt untimely, end evokes the melancholy claustrophobia of childhood denied.
Even more poignant are the two rooms and short walkway in which Sir Walter Ralegh spent almost two decades cooped up and writing soaring, unfettered prose, while the mean-minded James I made up his mind to deny him life as well as liberty. These still hold a few traces of the man himself, the rare "Black Swan", poet, explorer, historian, adventurer - and tutor to James's son. It's a small walkway for such a man to walk.
Beside such evidence of inhumanity, the dungeons and instruments of torture are almost mundane. Yet they too build up a picture, a picture of the lengths to which power has gone.
Sir Thomas More's cell is due to open next year in the Bell Tower as is a display of art associated with the history of the Tower.
The Tower was the first home of the Menagerie, which even in the 13th century contained lions, leopards, an elephant and a polar bear. In the 19th century it moved to Regent's Park to become the Zoo, but an exhibition in the Tower opening in October commemorates the centuries in which the massive stone walls resounded to the cries of exotic animals.
The Crown Jewels, perhaps the most popular of all with foreign tourists, still work their magic, eliciting cries of "ooh!" and "aah!" from children, who rush round to ride again and again on the travelator which trundles past the glass cases.
The Crown Jewels offer more flash, trash and dazzle than a mirror ball at a disco. Queuing visitors watch footage of the Coronation of Queen Elizabeth II, its majestic pace and formality. It is presented as a benign tableau, a piece of national theatre. But you don't have to see it like that.
Items such as the enormous gold epergne (dish), big enough for a small child to swim in and heavily embossed with lazy, luscious figures of nymphs and satyrs, or the huge gleaming silver platters, tell a story of unbridled and lavish extravagance. But these metal fantasia pale before the enormous, fateful jewels. The Koh-i-Noor, the Cullinan diamond, the sapphire of Edward the Confessor, the Black Prince's Ruby: these are pieces of mineral so intensely desirable that small wars have been fought to gain them.
The sovereign at coronation, draped in red and ermine fur, weighted down with crown, sceptre, orb and ring is more crystal than human. Perhaps this aspect of the jewels is best summed up in the "little crown" worn by Victoria in her last years. She was too frail to support the huge gold trappings of state so she had a lightweight version made. It is simply diamonds and sparkles like something made from dew-drops. But these are not dew-drops, children, they were dug out of the earth by undernourished black men, who died before their time so that the Great White Queen might not hurt her arthritic neck.
Well worth the price of admission, just for that sobering revelation.
Tower of London, London EC3 4AB. Tel: 0207 488 5681. Special rates for pre-booked school parties September to April. Education weeks and outreach sessions for local schools. 0207 488 5694. Classroom sessions 0207 488 5658. In high season, book in advance by post, writing to the Group Ticket Office