My Kenpo club holds a four hour belt ceremony workout on the beaches of Bodega Bay , north of San Francisco. While the location is scenic, from a performance aspect, moving on slippery sand is difficult, and everyone moves slower, in part due to caution and in part due to fatigue. There are often a few pulled groin muscles for those unaccostumed to working out on sand (probably all of us!), and that would cull away the older fighters. This wouldn't make for a good showing.
I liked Phil's suggestion of working out in the river overflows. That would make for a different gathering as folks would be less willing to go to the hard ground. My group tried fighting in a river runoff pump station, and the cement wasn't too bad.