My town doesn't have any off-leash parks so it's just not something we've ever done. Today, though, I discovered that there's a dog park 2 towns over, about a 10-15 minute drive away. It was a gorgeous afternoon, so I put Jack in his carseat and we headed over. We had such a good time!
When we first arrived there was only one dog there and they were heading home but decided to hang around for awhile and play. I think that worked out well, because Jack wasn't overwhelmed with chaos. A few more dogs came, then a few more, until at one point there were maybe 8 of them running around. Jack was by far the smallest (and likely the oldest; he's around 10 lbs and almost 14 yrs old) but he was keeping up with the "big dogs" and having a wonderful time.
In the past, Jack has never really been around large numbers of dogs. He hangs out with my neighbor's old golden, but they don't really play, just share the yard. He hangs out with my father's BC's, but they don't really have time for him and he can't keep up with them so they don't play. He's been with friends' dogs, but generally not more than 1 or 2 at a time, so I was a bit wary of taking him somewhere with so many new dogs. I'm so glad it went well. We'll certainly be going back.