It's night and a man and woman are searching for something in their rover. She gets out, and falls in very deep undulating dry quicksand. He uses a rope from the rover to get her out. Later, it turns out the only way into an underground chamber they are looking for is to swim through and under the quicksand (using scuba gear I think?).
I know there's a clip on YouTube somewhere, but I wasn't able to find it
