Doug Lombardi has been fairly vocal about what gamers can expect from Half-Life Episode 3 and has made it clear that players should not expect to visit City 17, at least not in Episode 3.
Speaking to EuroGamer, Mr. Lombardi mentioned that, Pre-production is definitely going, and it'll be ramping up rather quickly now that they're ramping down on Episode Two. According to the Valve Marketing Director, the people working on Episode 3 are also trying to complete Episode 2 in time for its scheduled, October 2007, release.
Recent rumors that Episode three will find Gordon Freeman involved in an epic climax in an Arctic research station were not denied by Doug Lombardi while programmer David Speyrer added, we're not going to spoil it. No matter what Doug said.
It's hard to decide what to expect of Episode 3 when the details of Episode 2 are not yet out there but it seems that there will be no further look at City 17 in Episode 3 although Mr. Lombardi made sure that we knew that Gordon will eventually return, I don't think you'll head back to City 17, for sure, not in Episode 3, anyway, he said.