Every morning at 9am, a military guard escorts the keys to the Tower and its huge wooden doors yawn open again for outsiders. It’s the most famous castle in the world, a UNESCO World Heritage Site, and a symbol of not just London, but also of a millennium of English history. Less a tower than a fortified mini-town of stone and timber, its history could fill this book. Suffice it to say that its oldest building, the four-cornered White Tower, went up in 1078, and the compound that grew around it has served as palace, prison, treasury, mint, armory, zoo, and now, a lovingly maintained tourist attraction that no visitor should neglect. Exploring its sprawl should take between 3 and 5 hours. 
The key to touring the Tower is to arrive close to opening, since intimidating queues can form by lunchtime for the Crown Jewels, located in the Waterloo Block at the north wall (farthest from the Thames), and the White Tower, in the center. Tickets are sold outside the battlements. Hit the Welcome Centre, just past the Ticket Office, and grab a copy of the free “Daily Programme,” which runs down the times and locations of all the free talks, temporary exhibitions, and mini-performances. Plenty are offered—the Tower at times feels like a theme park with 1,000 years of history behind it. As soon as you’re in, between the Middle and Byward towers, note the next time of the prime excursion: the 1-hr. Yeoman Warder Tour, led with theatrical aplomb by one of the Beefeaters who live in the Tower and preserve it. (There are about 100 Tower residents, including families, but only one of the 35 Beefeaters, Moira Cameron, is female.) The tour (don’t come later than 2pm if you want one) is engaging, but juvenile—expect bellowing and histrionics, each reciting an identical script with a gleeful fetish for yarns about beheadings and torture. (In truth, you can count the people executed inside the Tower on your fingers and toes; it was considered an honor to be killed here, since it was private.) If you’d like your history delivered without vaudevillian shenanigans, head to the gift shop on the right after Middle Tower and grab an audio tour (£4), but do it early; headsets can run out. The official guidebooks (£5) here are pretty good, and they certainly help with orientation.
As you enter the Crown Jewels exhibition, you’ll see archival film of the last time most of the jewels were officially used, at the coronation of Queen Elizabeth in 1952. After passing into a vault, visitors glide via people-movers past cases of glittering, downlit crowns, scepters, and orbs worn (awkwardly—they’re 2.3kg/5 lb. each) by generations of British monarchs. Check out the legendary 105-carat Koh-I-Noor diamond, once the largest in the world, which is fixed to the temple of the Queen Mother’s Crown (1937), along with 2,000 other diamonds; the Indian government has been begging to get the stone back. The 530-carat Cullinan I, the world’s largest cut diamond, tops the Sovereign’s Sceptre with the Cross (1661). The Imperial State Crown—ringed with emeralds, the 170-carat Black Prince’s ruby, and diamonds aplenty—is the one used in the annual State Opening of Parliament; the solid gold St Edward’s Crown is for coronations. After those come candlesticks that could support the roof of your house, trumpets, swords, and the inevitable traffic jam around the 1mwide Grand Punch Bowl (1829), an elaborate riot of lions, cherubs, and unicorns that holds 144 bottles’ worth and shows what it would look like if punch bowls could go insane. Because Oliver Cromwell liquidated every royal artifact he could get his hands on, everything dates to after the Restoration (the 1660s or later). Clearly, the monarchy has more than made up for the loss.
The four-sided White Tower (completed in 1098) is the heart of the fortress, and for more than 200 years, it was the tallest structure in London. Touring its four cavernous levels requires much circuitous stair-climbing, but takes in a wide span of history, including a fine stone chapel, Normanera fireplaces and toilets, the gleaming Line of Kings collection of the Royal Armoury (even small children can’t help but notice the exaggerated codpiece of King Henry VIII’s intricately etched suit from 1540), and some models depicting the Tower’s evolution (it’s been much altered, but the six smallest arched windows on the White Tower’s south side are original to the 11th c.). Try to time your arrival on the top floor to take one of three daily tours (10:45am, 12:45pm, or 2:15pm) of the nearly 1,000-year-old Chapel of St John. After you’re finished in here, you’ll have an excellent overview of how the whole complex worked. 
Once you’ve got those two areas under your belt, take your time exploring the rest. I suggest a stop in the brick Beauchamp Tower (pronounced beech-um, built in 1280), where important political prisoners were held and where you can still glimpse graffiti testifying to their suffering. In front of it on Tower Green is the circular glass memorial designating the Scaffold Site, where the unlucky few (including sitting Queens Anne Boleyn and Lady Jane Grey) are said to have lost their heads. In reality, we don’t know exactly where they were killed, but Queen Victoria wanted a commemorative site set, and because of the evident dangers of displeasing the monarch, this spot was chosen.
The St Thomas’s Tower, from the 13th century, is closest to the Thames and re-creates King Edward’s bedchamber with authentic materials. Beneath it, Traitor’s Gate, once called Water Gate, originally was used to ferry prisoners in secret from the Thames. Torture was never a part of English law, but it happened here anyway, and the Bloody Tower was where some of the worst stuff went down. In truth, there were only 48 recorded cases of torture in the Tower, but that doesn’t stop curators from devoting an entire room to a display of (mostly replica) torture devices.Don’t forget to climb the ramparts for that classic photo of the Tower Bridge. Skip the Royal Fusiliers Regimental Museum, a dreary hodgepodge of military memorabilia. 
Daily at 2:50pm, the guards parade outside the Waterloo Block to the Byward Tower. On Sundays, your admission ticket allows you to attend services at the Chapel Royal of St. Peter ad Vincula, the Tower’s church with a Tudor-era Spanish chestnut ceiling, at 9:15 or 11am; otherwise, the only way to get in, and to see the marble slab beneath which Boleyn and Grey’s decapitated bodies were entombed, is with a Yeoman Warder Tour—salacious tales of gory fates are spun virtually on top of the graves of the people who suffered them, which by any measure is tacky. It’s a shame the cheap histrionics of the interpretation strip this ancient Tower of so much depth and dignity