Our gym's lock-in is the highlight of the year for a lot of our gymnasts.  On a nearby Saturday we meet around 3pm at the gym.  We all go together to a corn maze/pumpkin patch...cider, donuts, feeding the animals...each gymnast getting to pick out out a small pumpkin.
 
Back to the gym after for pizzas & pumpkin decorating (markers).  The kids then parade around the floor in their costumes...a little 'competition' (where all get a prize).
 
After dark we split into two groups;  the younger ones to a less scary haunted train ride, the older ones to a haunted woods.
 
We all get back to the gym after an hour or so, where we have a DJ set up on the floor.  Lights out, disco lights on...and the kids go crazy dancing around for a couple hours.  "Lights out" at midnight, but of course most of them are up & about until the wee hours.
 
We usually have 6-10 parents stay over too - as much fun for us as the kids I bet.  Other than carpooling & keeping everyone safe and out of trouble, we end up staying up most of the night playing cards, etc.
 
A great time for everyone