Note the multiple layers of defensive walls. The tall building in the back is the keep, called the White Tower.

After paying a, ahem, kingly sum to enter, you proceed across a bridge over what was once a moat.

Metal sculptures throughout the Tower represent the soldiers who once defended the castle.

Passing through the first wall, you're greeted by this long building, which at one point housed the Royal Mint around the time it was run by Isaac Newton.

Not just defensive walls and a keep, the Tower consists of many buildings both within, or in this case, attached to, its walls.

This is Water Lane, which extends the length of the Outer Ward on the river side of the castle.

Water Lane looking back towards the entrance (and where I took the last photo) from roughly mid-way.

The infamous Traitor's Gate, mentioned in many books of history and fiction, not least Neal Stephenson's epic Baroque Cycle (I saw no signs of Enoch Root anywhere).

The area above Traitor's Gate was once a series of richly appointed rooms...not that you can tell that from this picture.

Ah, that's more like it. It's a massive room by the standards of the era. I'm standing roughly in the middle.

It amazes my British friends that so many Americans think this is called "London Bridge."

You don't even notice you've crossed a bridge over Water Lane to Wakefield Tower. Built by Henry III in the 1220s, it's one of the oldest parts of the castle.

Three of the most iconic symbols of the city: Tower Bridge, the Tower and the Shard (Big Ben is farther up the river).

The Inner Ward, with the White Tower. The wall on the left is one of the original walls of the Innermost Ward.

A metal knight stands ready to attack those who approach Salt Tower.

Salt Tower was once a prison for many important men. Some of their words remain scraped into the walls.

Looking inward, it's like looking back in time. Look outward, and the contrast with the modern world is stark.

This was posted on the wall. Can't say I disagree...

With this view especially, I wonder what the many builders of the Tower would think of London today, and that their castle is now pretty much solely a tourist attraction. (Editor's note: That brick building on the right edge of shot, once a warehouse, used to house CNET's UK offices.)

You want to get shot by an arrow, buddy? That's how you get shot by an arrow.

These ravens are big. The size of cats. They make spooky noises. They do not care about you. Legend has it that should they fly away, the monarchy will fall and Britain with it. Hence their wings being clipped -- they can't fly away.

The Shard peaks out from over the wall, looking in on someone's...laundry?

The Yeomen Warders, aka the "Beefeaters," can actually live in the castle.

The Waterloo Block is home to Jewel House, where the Crown Jewels are kept. No photos allowed. Spoiler: they're shiny.

The White Tower on the left, with Tower Bridge in the distance.

The picturesque Tower Green. Watch me ruin it: A few queens and some other nobles were beheaded here. Before that it was a burial ground.

Though not as sprawling as the Citadel of Carcassonne, the Tower of London is pretty massive and, today at least, has a lot of open space.

One of the old walls of the Innermost Ward. Up next we head to the keep.

The interior of the White Tower has been converted almost entirely to a museum.

Suits of armor from various kings are on display.

These are not, as commonly believed, the knights who say "ni."

This space was used for a variety of different things throughout its life. Originally it was likely part of the royal apartments. Later it was used as an armory, magazine and today, a museum.

All told it's a pretty fantastic view, though I bet it was drafty when new.

Interestingly, it's not just English and British artifacts. There's even samurai armor on loan from a museum in Japan.

Keeper seemed friendly, if a little cold.

But seriously, who stores gunpowder with a dragon? Think people, think!

Between the main room and the outer wall there were passages like this. Might have helped a bit with insulation and protection.

All in all it's a great museum, and a fascinating look back into what life was like during the many ages of the castle.

After heading down (many) stairs, you'll find rows of cannon and mortars in the basement.

Throughout the day there are many events. This one, as I left the White Tower, marched from here down towards the river.

Cradle Tower was once a private water gate for Edward III. None of those public water gates for old King Ed.

A wooden dock extended out into the river, though now the land has been reclaimed and the river is farther away.

Porters had lodges, so they could be ready to help the king when he wanted to jaunt up or down the river.

More cannon for defense of the castle, now plugged and decorative.

As I exited, I noticed a small series of rooms where the Royal Mint once was. The coinage was rather fascinating, as was Isaac Newton's involvement.

There was no mention of Jack Shaftoe.

A Yeomen Warder making his way down Mint Street.

I recommend heading out and passing between the river and the Castle for a last few looks, then heading towards Tower Bridge.

One last look at Traitor's Gate, this time from the other side. It would probably look a lot cooler with water.

The view of Tower Bridge from the Queen's Walk next to the Tower. I cribbed this from my Instagram.

To round out your day, keep walking towards the Shard (you can hardly miss it), and check out the view from the top. I recommend watching the sun set over the Tower, the bridge and the rest of this amazing city. (This is from my Instagram too.)

For the full story behind this tour, check out The Tower of London: Take a look inside.