DANA WIELUNS LEGAWIEC, David Greenham and Xander Johnson, from left, in a scene from the Bath Shakespeare Festival’s “Twelfth NIght” production, which opens July 20. BSF, a fully professional theater, will present Shakespeare’s “Twelfth Night” outdoors in City Park on Saturdays and Sundays from July 20 through Aug. 4. The “curtain” rises at 7 p.m. The per formances are presented in conjunction with the Patten Free Library. Some consider “Twelfth Night” to be Shakespeare’s greatest comedy. It is the ultimate comedy of mistaken identity, in which a girl disguises herself as a man to be near the Count she adores, only to be pursued by the woman he loves — and whom he has asked her to woo on his behalf. It is a per fect outing for families, with its outrageous stor y and unforgettable characters. Tickets are $15 for adults, $10 for students and senior citizens, and $5 for children younger than 5, and are available by calling 854-8882. In the event of rain, the show will go on at Bath Dance Works, 72 Front St., Bath. For details on weather, visit bathshakespeare.org.