It was there in December 2009 that high hopes for a legal pact to curb climate-harming greenhouse gases came crashing down as diplomacy foundered in extra time.
Now, six years later, 195 nations will try again, this time in Paris.
Much has changed in the climate arena since 2009, and observers say there is reason to be hopeful that negotiators may finally seal some sort of deal.
"The world has learned some valuable lessons from the experience in Copenhagen," former US vice president turned climate activist Al Gore told AFP.
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When leaders failed to reach consensus six years ago, a handful among them -- representing key players such as the United States, European Union, Japan, China, India and Brazil -- huddled together to thrash out a face-saving "accord".
Instead of ratifying it, shell-shocked delegates simply "took note" of the non-binding document -- an event French President Francois Hollande remembered this week as "an immense failure".
"It was the worst moment in my life," Maldives negotiator Amjad Abdulla told AFP.
"You can't just... Pick... Some people and say this is the draft, take it or leave it. That's what happened in Copenhagen."
To avoid a repeat, summit host France has opted to leave heads of state out of the nitty-gritty haggling over text.
Instead, they will give back-to-back speeches on the first day of the November 30-December 11 marathon, seeking to imbue it with a sense of mission.
Bureaucrats who have been hammering out a blueprint for the last six years will take a final stab at drafting, and then leave it to ministers to seal the deal.
"This is the first time before a COP that we have such a small text. Before Copenhagen we had 300" pages, France's climate negotiator Laurence Tubiana said.