The noise is unmistakable, even when you don't expect to hear it. It's a gentle roar that rises every now and again; it bubbles with passion.
It seems so out of place here in the market, where most of the sounds are of vendors entreating you to relieve them of their wares. Below that is the normal hubbub of tourists stocking up on their Peruvian souvenirs, the colourful beanies and mass-produced T-shirts.
But deep in the background there's that noise, that distant hum of action, so I decide to follow it, to see if it really is what I think it is.
Out on the street it's been raining - the river here in Aguas Calientes is as strong as ever, rushing past the town with a promise of violence that seems strange in such a beautiful place. Slip in there at this time of year, during the rainy season, and you'd be in serious trouble.
Bus after bus rolls through the little town's narrow streets, dropping passengers off and preparing to ferry yet another load up the hill to Machu Picchu, the sight everyone is here to see. Brakes groan, doors squeak, people file on and off.
There's no other reason to come to Aguas Calientes, nothing else to do here but wander through those tourist markets and select something to remind you of your visit to Machu Picchu. It's a Sunday afternoon but it's business as usual in town - the tourist trade here never sleeps.
The sound seems like it's coming from up the hill, away from the train tracks and the main square. Not many gringos make it up there, because there's no reason to. There are just a couple of local restaurants of questionable quality and blocks of apartments. Nothing much to see.
I'm almost certain I'm right now - the sound has joy in it, and passion, but also a little fury. Two kids dash past me on the cobbled alley, making their way up the hill, and I'm sure it's what I think it is.
Sure enough, I round one last corner, past one more block of flats, and there in the middle of Aguas Calientes, not two blocks from the tourist markets and the bars but hidden in another world, is the local football pitch. It's perched on the hillside right in among the city, carved between the buildings and alleys and squares.
The noise is from the crowd, the large group of locals who've gathered outside the high wire fences that surround the pitch to cheer on their local team. No one pays any mind to the gringo in their midst - they're engrossed in the game, in chatting to each other, in eating their food and drinking their beers.
It might sound stupid but I've found my holy grail.
This morning I'd been in Machu Picchu, the Incan ruins that must top more bucket lists than almost any sight in the world. It had been fascinating, of course. A lifelong highlight. But I like my culture living and breathing, which is why I'm just as happy having stumbled upon a local football game as I was stumbling across ancient ruins just a few hours earlier.
This is fun. I can't even tell which team is the local one, until the guys in blue score a goal and no one cheers. Right, so we're going for the pink team then. The people around me don't seem too bothered by the score - this is a social event, the game comes second.
I don't speak Spanish, so I'm not joining in the conversation, but still, there are few global unifiers quite like football. Put it up there with music, or dance, or food, or a simple smile. Doesn't matter where you go in the world, if you know football, you've got something in common with everyone.
I know when to cheer. I know who the bad guys are. I know we hate the referee. And I know that here, very briefly, until the guy in black blows the final whistle, I won't be treated as a tourist. I'll just be a fan.
The setting is spectacular. The Andes rise steep and imposing on all sides of the narrow valley. The synthetic pitch is a raw, striking green among the drab greys and browns on the buildings.
The crowd, perched on concrete benches or standing with fingers curled around the wire fencing, is a sea of colour, from their beanies to their knock-off football jerseys of teams from around the world. They're still chatting, or cheering, or some even singing.
With just a couple of minutes to go, the pink team - our team - scores, sending the crowd wild. The guy on the bench next to me throws an arm around my shoulders, gives a high salute to the gods of the beautiful game. I'm doing exactly the same.
You don't expect to top a visit to Machu Picchu in a lifetime, let alone that same day. But strangely enough, I might have.
Do you prefer interacting with locals to seeing the sights when you travel? What have your memorable experiences been? Post a comment below and share your stories.