Rucksacks are trampled underfoot and there is the distinctive crunch of some hapless child's crayons as you unwittingly apply your full weight.
A party of Japanese tourists will politely but resolutely get to the front led by a perfectly diminutive female with a squeaky voice that doesn't quite rise above the general hum and trying to get attention by waving a collapsible umbrella.
She has been here before and knows the drill.
As she strains to make herself understood there will be a frantic nodding of big flowery sun hats direct from a fashionable ladies outfitter in Osaka or Tokyo.
Accompanied by the sound of mature ladies in agreement as they are let into the secrets of the initiated.
At the back are the uninterested men who have been to five art galleries in three days.
They have reached saturation point and don't even have the willpower to pretend any more.
Unimpressed American families 'doing Europe' with bored teenagers in tow whine amongst themselves; "what the heck is all the fuss about, where is the cafeteria, wasn't there a McDonald's across the road"? And on it goes, all day every day.
As you walk along the upper gallery of the Museo del Prado in Madrid you might look into room 12 and see a crowd of tired and bewildered tourists looking at a gigantic picture that dominates the room.
The Spanish People own one of the most revered and studied paintings in the entire body of Western art.
Visited by millions and studied by academics all over the world, 'Las Meninas' is a strange painting indeed.
This is a treasure of the Spanish Nation and you are now going to be enlightened.
At first glance the picture seems like a fairly straight forward group portrait or 'conversation piece' but there is far more depth to this picture than just simple documentary illustration.
The title of the picture tells us that it is about 'Las Meninas', (the maids of honour), and certainly they are pictured, centred around the Infanta Margarita, the daughter of King Philip IV of Spain and his first wife Elizabeth of France.
Along with Infanta is the usual retinue of jesters and dwarfs including two hired in playmates and a sleeping mastiff.
Behind her is the chaperone party made up of a monk and a nun to look after her physical and spiritual welfare.
So far so good, but this is where the picture gets interesting.
Velsquez has made this into a self-portrait for it is he shown looking out at us from behind the canvass.
He is shown painting a picture, maybe this picture you are looking at now and Margarita and her retinue are simply here to check the progress.
If that is so, who are the people shown in the mirror on the far wall? Could they be the King and Queen having their portrait painted? The 'ground plane', that is the surface Margarita is standing on, could be imagined to extend into the space you the viewer is occupying.
If that is so, then you could be one of the characters in the mirror.
Velsquez is looking out of the picture directly at you as you stand there.
Indeed the faces in the mirror are painted so indistinctly that they cannot be identified as anyone in particular and some scholars assume it is the King and Queen.
So, the question is, exactly who is being painted? Another mystery is 'The Cross of the Order of Santiago' that Velsquez displays on his tunic in bright red.
Awarded to him by the King three years after the picture was painted it is said that the King himself was allowed under the direct supervision of Velsquez to paint on the cross himself.
Added to this enigma is the question of who is the gentleman in the doorway? There is some considerable debate about this.
One theory suggests this is Velsquez's brother who was the keeper of the King's tapestries.
No one had ever done this with a royal portrait before.
No one had ever dared to be so clever and inventive with a Royal commission in the entire history of art.
When you are in an art gallery and looking at endless, pointless rows of painted royalty, whose only excuse to be painted at all is their birth, think of this picture by Velsquez who has made the subject much more interesting.
Decoding this picture is a fascinating activity and is an insight into an intricate mind.
The painting is not exactly as Velsquez left it in 1656.
It was damaged in a fire in the Alcazar Palace in 1734 and had some material removed from the sides and there has been several attempts at cleaning and restoration.
Crowds of visitors are degrading the picture, but nevertheless, it hangs in the Nations Capital as one of the premier treasures of the country.
Just as a final anecdote, sit in the Plaza Oriente in Madrid in one of the very posh caf bars on the same side as the Opera facing the Palace.
Have the most expensive caf con leche of your entire life with the waiter wrapping an especially warmed blanket around you wife's knees.
Look up and you will see a yellow lozenge-shaped tin plaque on the wall of one of the very fine buildings facing the palace.
It states that this was the house of Velsquez.
Wonderful, what an artist.