This is the set for the inside of the mercave. This is where the merfolk, characters in the show, live. Actors will open up the doors of the caravan so you can see the inside, like this picture, near the end of the show.
During the show, the actors will ask for assistants from the audience to come and help with pulling a red ribbon out of the caravan. You can volunteer to do this, but you don’t have to. The ribbon will be passed to the audience member by the giraffe puppet, and then they will pass it to another audience member.