Füssen has two distinct high seasons. June to September is the warm-weather window when the lakes are open for swimming, the Forggensee boats are running, the mountain cable cars are operating, and the Marienbrücke above Neuschwanstein is open. July and August are also when the castle crowds are heaviest — book tickets weeks ahead.
December to February turns Füssen into a small Alpine winter destination. The Forggensee is drained but the surrounding mountains have downhill skiing (the small Tegelberg resort, with bigger areas at Reutte and Garmisch within an hour), cross-country trails in the Pfronten valley, and the castles dusted with snow look exactly like the postcards. Some cable cars close in November and again in May for maintenance, and the Marienbrücke may be closed for ice.
The transitional months — late April to mid-May, and October — are the quietest. Crowds drop sharply, hotel prices fall, the castles stay open, and the weather can be either of two seasons depending on the day. October has the best autumn colours in the lower forests.