When rain falls on the sukkah, one is not required to stay inside. The Mishna in Sukkah 28b compares rain falling on a sukkah to a master who receives a drink from his servant and then throws it back in the servant's face. The analogy is that through the rainfall, God is showing His displeasure with our performance of the mitzvah by not allowing us to fulfill our obligation of sitting in the sukkah. In Israel, it is common practice for hotels, restaurants, snack shops, and outdoor tourist attractions (such as zoos) to provide a sukkah for customers to dine in.