Googling shows that a deep-space EVA was done to retrieve film canisters on the return from the moon. It does not explain, but I assume “deep-space” means outside of earth orbit. Which raises the question: Why were the film canisters outside in the first place?
The film canisters were in a bay of the Service Module behind the command module. Someone realized that they could move stuff around back there and have room for high resolution cameras and even a bay to launch a sub-satellite. Since the Service Module does a swan song into the atmosphere at the end of the mission, Al got to take a 38 minute walk when they were coming back from the moon.
During a presentation Al said the following: “I grew up on a small farm near Jackson. I didn’t want to stay on that farm. I wanted to get as far away from that farm as I could. I just never realized how far away I would get!”