Bid teams from Chicago, Rio de Janeiro, Tokyo and Madrid converged here in conjunction with IOC executive board meetings and the world track and field championships, attended by as many as 60 IOC members.
"You can see people just walking through the lobby," Ryan said. "It's a chance to build and expand on those relationships."
Ryan has met most of the IOC's 106 members over the past few years of the campaign, but will not pass up a chance to talk to them again, especially with so many in one place at the same time.
"This is the last opportunity," he said. "You want to meet as many as you can right up before the vote. I say, 'Let's get together and have coffee or something."
Before an interview with The Associated Press, Ryan stopped several times to greet IOC members. Later, a powerful IOC official -- Olympic Games executive director Gilbert Felli -- walked past and said hello.
Chicago has been considered a strong contender in its bid to bring the Summer Games back to the United States for the first time since the 1996 Atlanta Olympics. However, Rio has made a big impact with its energetic and emotional appeal for the Olympics to be held in South America for the first time. It's seen by some as the current favorite.
"There's a lot of discussion that Rio has gotten stronger," Ryan acknowledged.
Yet the momentum can swing in the final weeks, days and hours of the race.
"I've said all along that there are four great cities," Ryan said. "From my perspective, there's going to be ebbing and flowing on where people are. At one point everybody's talking about city A, then city B.
"People have their predictions about who the finalists are going to be. I suppose if you've got 99 people in a room, you get 33 that say one thing, 33 that say another and 33 that say another."
IOC host-city votes are conducted by secret ballot and can be highly unpredictable. The city receiving the fewest votes is eliminated in each round until one emerges with a winning majority.
The first round can be extremely tricky, with sympathy votes and other factors that can put a favorite in danger of going out. Assuming no city will win in the first round, the second-choice votes will be crucial.
"I'm appropriately worried," said Ryan, looking relaxed in a blue blazer and open-neck shirt. "I think it's very, very tight. People have all these predictions. But I predict a really, really tight vote all the way through."
Ryan has studied past Olympic votes, including the 2005 ballot in which London overcame the perceived favorite Paris in the final round.
"What's come clear to me is that you probably don't want to be the favorite going into the vote," Ryan said. "Sometimes people interpret actions and behavior maybe different than they're intended or different than they really are. There seems to be a momentum that's hard to predict."
The largest number of members come from Europe, but votes from Asia, Africa, the Americas and Oceania are also crucial.
"It's an independent body, I'm impressed by that," Ryan said. "I was a little bit surprised. Early on I heard a lot about bloc votes, but I don't believe in bloc votes. I think they all make up their own minds."
The wild-card factor could be the appearance of heads of state and government at the IOC meeting.
Brazilian President Luiz Inacio Lula da Silva and Spanish King Juan Carlos have announced they are going to Copenhagen. The crown prince or prime minister of Japan may come. The biggest question of all: Will President Barack Obama be there?
Obama calls Chicago home, has appeared in videos supporting the bid and has set up a White House office for Olympic and youth sport.
His presence in Copenhagen could be decisive, just as Tony Blair helped secure the 2012 Olympics for London when he lobbied IOC members in Singapore in 2005 and then-Russian President Vladimir Putin pushed Sochi's winning bid for the 2014 Winter Games when he traveled to Guatemala City in 2007.
Ryan said the decision will be made by the White House depending on the situation of the time.
"We just don't have any sense of what his schedule will be," he said. "We know this: that he is a passionately strong supporter of the bid, and he's a really strong believer."
Chicago's bid has been clouded by thorny relations between the IOC and the U.S. Olympic Committee over the American body's share of Olympic revenues and, most recently, the USOC's plans to launch its own Olympic television network. The IOC said the USOC acted "unilaterally" hastily and the TV project could undermine Olympic network NBC.
USOC chairman Larry Probst met with IOC president Jacques Rogge in Berlin last weekend and announced the TV project was being put on hold -- meaning the dispute shouldn't be ongoing during the vote in Copenhagen.
Another key challenge for Chicago is to convince IOC members -- and taxpayers back home -- of its budget plans and financial guarantees for the games. Chicago Mayor Richard M. Daley has pledged to sign the IOC's host city contract if Chicago gets the games, taking full financial responsibility for any deficit.
"I think the IOC has to be pleased that we have every intent of signing the host city contract," Ryan said. "At that point you're putting your city's credit on the line. Chicago has a very strong credit rating. Then, for the protection of the taxpayers and for the comfort of the IOC, we're putting an insurance package together."
But that's down the road. In a few weeks, the only numbers Ryan will be interested in are the IOC vote totals.
"I've learned three important lessons from IOC members," Ryan said. "Don't assume anything, stay humble, and work, work, work right up to the very end."