Retrieving the Space Shuttle's Solid Rocket Boosters
After each Space Shuttle flight, NASA retrieved Solid Rocket Booster (SRB) segments from the ocean. During a Shuttle launch, the SRBs detached as the Shuttle rose, and they fell into the ocean, where teams in two massive ships (Liberty Star and Freedom Star) were waiting to locate and retrieve them so they could be reused. Here's video of NASA's SRB recovery teams picking up the segments after the STS-133 launch, the final mission of the Space Shuttle Discovery in February 2011.
Although I've always known the SRBs were reused, I never saw footage of the retrieval process. This is pretty much raw footage of the process (no narration), but if you're a space nerd, this is a must-see video. Part of the fun is seeing just how massive these things are; the other extra-fun bit is the time-lapse at the end, which helps to show how long the process takes.
If you want more of that, there's a 45-minute video of the STS-135 retrieval. It's slow, but shows even more of the process.