The dry season — May to September — is the comfortable time to visit Ambarawa: cooler air at altitude, clear mornings, and a good chance of seeing Merapi and Merbabu from Gedong Songo. The wet season (November to March) brings dramatic skies and very green countryside but also heavy afternoon rains that can shorten visits to the temples.
The Battle of Ambarawa anniversary on 15 December draws crowds to the Palagan monument; otherwise the town is quiet outside school holidays.