"What's on sale in October is Europe," says Peter Greenberg, author of "Tough Times, Great Travels: The Travel Detective's Guide to Hidden Deals, Unadvertised Bargains, and Great Experiences," and travel editor for CBS News.
Bilateral agreements are the reason, he says. Those are the agreements nations make on "just how many seats they must fly between countries," he says.
And, in the fourth quarter of the year, airlines can't just cut flights, because "that would violate the agreement," Greenberg says. So they cut prices instead for travel near the end of the year.
That airline ticket from New York City to London that went for $1,900 this summer will cost about $480 by Oct. 1, he says. You still have to shop smart. "It's not on every seat, and it's not on every flight," he says.
You'll experience a different side of Europe than you would have earlier in the year. "The weather's nice," Greenberg says. Plus, "there are no crowds, no lines, better service and better deals. The fourth quarter is always great."