It's the "second annual five-company Shakespearian Secret Dessert Theater"! The last two nights of it are tonight and tomorrow night.
Apparently you show up at a trolley stop in Philadelphia at 7:30 p.m. wearing a red carnation, and at 8 p.m. the hosts take you to the Secret Theater, where you can buy tickets (if still available by then).
The website explains:
Each act of KING LEAR happens in a different space, performed by one of 5 different theatre troupes from around the country, and served with 5 desserts.
Oh, yes, and they also provide beverages, both alcoholic and non-.