The Heron’s architect was N. D. Austin, a 31-year-old artist known for what he calls “trespass theater.” “It’s about making the invisible visible,” he said of his philosophy.

Mr. Austin located a suitable water tower by scouring Buildings Department records for violations with egregious scaffold fines. That can indicate a neglectful landlord, he said, which meant it might be a vacant building ripe for adopting as one’s own.

One Saturday night last month, 12 guests squeezed through the trap door into the space. “The great thing about the upright bass is how it got up here,” said Dirby Luongo, one of Mr. Austin’s collaborators who played the doorman. “It’s like a ship in a bottle.”

At one table, a first date was in progress. Chelsea Cammarota, 35, explained that she and her date did not know each other well. “He sent me a photo of a clock,” she recounted. “I said, ‘I’ve seen a lot of “Law and Order.” ’ ” Nevertheless, her date, Steve Showalter, told her, “We’re going to do something fun.” But he was clueless, too, running on blind faith in the friend who had given him the watch.