Archive.org came through with another all-time favorite!
Where Eagles Dare was directed by Brian G. Hutton, and was based on the novel written by Alistair MacLean. The setup is a rescue mission; A brigadier general is being held captive and interrogated in a Bavarian mountaintop castle by the Nazis, and the SOE tasks Major John Smith (Richard Burton) with leading a team of commandos to bust him out.
Where do I even begin with this film? It has everything you'd want in a WWII spy thriller; the slowly building suspense is absolutely masterful, not a single actor was miscast and everyone put in a damn good performance, the locations, the way the plot unfolds, Gah! I can't say enough good about it.
It was filmed on location in Austria and Bavaria, which results in some really lovely authentic shots of snow covered peaks and towns. The cinematography is workmanlike, perfectly capturing the important bits but never lingering for an artistic shot, which serves the movie well.
The first time I saw it, I was surprised how relatively strong the women characters in it are, an uncommon sight for that period.
For the 60's, this is just a god dang masterpiece, right up there with The Great Escape, and IMHO is one of the finest WWII films ever made. A slow burn with an incredibly satisfying finish. Give it a shot, you won't regret it!