An endless throng of tourists, performers and pavement diners. Few notice the four-strong team of therapists and psychotherapists - one an Englishman in a kilt - weaving their way through the crowds.
Steve Potter, Dr Jamie Kirkland, Dhuana Affleck and Emily Baron are here to map our national psyche; to ask native Scots and overseas visitors what they think of the country, and to work out their hopes and fears for the nation. The key question - what is your relationship to Scotland? - is given added relevance by next year's independence referendum.
This kind of social mapping is known as Cognitive Analytic Therapy (CAT). Potter, who is based in Manchester, has run similar projects in Poland and Finland. He teaches psychotherapy in many parts of the UK and internationally as chairman of the International Cognitive Analytic Therapy Association.
People's answers are noted on an A3 sheet of paper, where they coalesce into clusters of disparate but linked thoughts. The Edinburgh replies formed the basis of a workshop that night.
First up is a young man in his late teens, who is holding a sign directing people to a nearby restaurant. "How do you see yourself?" asks Kirkland, the man in the kilt, who is a consultant clinical psychologist at the Royal Edinburgh Hospital's Orchard Clinic.
The young man says he sees himself as Scottish, but adds: "I wouldn't vote for Scottish independence - I believe we're better as part of the UK." He might not even vote "because I don't feel informed enough. I wouldn't say I'm not interested - it has a great bearing on the country, obviously. I don't know enough to make a decision either way."
Asked what he really wanted for Scotland, he said: "The economy to improve, more jobs for younger people." As a country, it accounts for itself "pretty well" in world terms, he thought.
Lauren, from Stirling, is in her twenties, and part of a young theatre group. She says she is proud of, and open about, her identity - she likes to wear tartan - and supports a broad, inclusive view of being Scottish. She says: "We can still be very Scottish and support the union if we want to."
Nearby is Scott Kyle, 30, who in 2010 won the best actor award from The Stage for his role in a Fringe production of Singin' I'm No A Billy He's A Tim. He is here to promote his latest play, Bad Boy Eddie, as well as How to Make a Killing in Bollywood, a co-production between his NLP theatre company and Bathgate's Regal Theatre, where he works.
Potter asks if Kyle is going to vote in 2014. "I don't know how to vote," he responds. "I genuinely don't know." Potter presses him: what do you need to know? "The correct information," he responds, "but I don't think we are ever going to get that."
He added: "The bottom line is, any country in the world that has oil is normally wealthy. Scotland isn't, because it gets ploughed all the way down to London. It's like having a mansion to maintain. We've got a wee house - but if we had the money, we could look after the house and make it nice."
When you're away from Scotland, Potter asks, is your relationship with Scotland different?
"It's brilliant," says Kyle. "When you go away, you realise how amazing it is. I was in Milan, touring Romeo And Juliet, for five weeks, and I kept saying to people, 'See in Glasgow…? See in Glasgow…?' and a guy said to me, 'Scott, you're no' in effing Glasgow any more, shut up about it!'
Scott Henderson, 27, who works for a travel website, said he was a Leither first, then from Edinburgh, then Scottish, then British. It probably complicates his voting intentions next year: "It means you think about things at a very local level sometimes."
How will he vote? "At the moment, probably no, and that's out of fear of what could go badly. I don't know what [the SNP] are going to do. No-one has told me what they're going to do. Until they tell me what they're going to do, properly and with detail, how can I vote for something that is going to change my life so dramatically?"
He sees Scots as a relatively positive people whose reputed dourness "is more a mannerism than the way we actually are".
Up near the castle, Adam Watters is dressed as William Wallace, his face painted in the style of Mel Gibson's Braveheart. He is a real tourist magnet.
"If we have a freedom and independence, we need to have our own monarchy," says Watters, who teaches 18th-century history in schools. "Our own parliament, our own monarchy. But we don't have our own monarchy, do we? … if we become an independent country, the Queen of England needs to become the Queen of Scotland, and she needs to be crowned up here."
He says he hasn't decided how to vote, but that Scotland "is quite a rich country and hopefully we shall have our own independence. My most important thing is jobs for the children - not for me, I have a job. A job for my son."
Linda, 53, from Glasgow, says she admires Scotland's breathtaking scenery: "You can be on your own as if there is nobody else in the entire world". Independence, she added, "might be quite scary - everything might become more expensive".
Another interviewee also called Scott Henderson, who lives on Skye, said he was neither for nor against independence, but was irritated by a line, allegedly coming from opponents of independence, "that we're too wee and too stupid [a country] to go it alone. In my opinion, we're neither."