Besides the ongoing levels in town buildings, the game also features temporary events.
Some events are alongside the main story in the town, while others involve completing levels inside buildings. The icons of active events are usually displayed on the left side of the screen. To start an event, all you have to do is tap on its icon.
Keep in mind that all events are time-limited. Once their time runs out, they disappear regardless of how much progress you have made. A timer showing how much time is left until the event ends is usually displayed on the event's icon.