If you don't know what Ginastica Natural is yet, it's a combination of BJJ-related movements, yoga, and other body-weight exercises. You can check it out on youtube.
Alvaro started by having us try to touch our toes. Some of us could, some couldn't. Then he ran us through a basic GN warm-up and had us try again. After just five minutes, most were much closer to touching our toes than before. Then the workout started.
Everything in Ginastica Natural is a combination of stretching a body-weight strength building, often simultaneously - and designed to complement your BJJ training. Often, Alvaro would show a GN technique, then demonstrate its relation to jiu-jitsu.
Breathing is another important piece of the puzzle in GN, and a great deal of time was spent on it. In fact, Alvaro maintains breathing technique is "the secret" to being able to train hard without getting run down. At age 56, he walks his talk. He could move better and faster than any of us, even though he's 20+ years older. Pretty inspiring to watch.
I definitely recommend attending one of his trainings if you get the chance. I believe it's a) a key to longevity of BJJ training, because all of us want to be able to move like Alvaro at his age, and b) it's really hard to get bored with this stuff.
Here's a video of Marcio Stambowsky (a level 3 GN instructor and friend of Alvaro Romano since they were teenagers) doing a brief Ginastica Natural workout