A pair of travelers are walking through woody terrain covered in deep snow, well dressed for cold winter. They reach some sort of bunker and go inside. There it turns out they are a man and a woman. The man throws some hi-tech fuel pellets into the room that cause a lot of heat, which makes the red-hued interior unbearably warm. The purpose of the heat is probably to fool the heat sensors. The heat forces them to remove all their clothing except for the underwear, and to pour over themselves some liquid to cool off, could be champagne. The woman asks why he hadn't warned her about the heat, and the man replies that she wouldn't have believed him.
They are there to break a safe. The safe has a keypad with a lot of keys, maybe even 10x10=100 keys. The man presses some of the keys in the appropriate sequence and appropriate pattern, and the pressed keys are lit up.
That is all I remember. It's a thriller from the 70's, but with those high-tech pellets and unusual safe protection thing this movie could also pass for sci-fi in those days.