The best time to visit Aachen is during the spring (April to May) and autumn (September to October) months, when the weather is pleasant and the city isn't overly crowded.
Spring in Aachen sees temperatures ranging from 10°C to 18°C, with the city's parks and gardens, such as the Stadtgarten, coming into full bloom. This is a lovely time for couples to enjoy strolls through the city and visit outdoor cafes. The slightly milder weather makes exploring the historic centre, including the Aachen Cathedral and Elisenbrunnen, very comfortable.
Autumn offers similar comfortable temperatures, usually between 12°C and 19°C, and the changing colours of the leaves add a scenic backdrop to the city. This season is ideal for those who appreciate cultural events, as there are often various festivals and markets. Families might enjoy the less intense crowds at attractions like the Carolus Thermen, making for a more relaxed visit.
While summer (June to August) is also popular, it can be busier with more tourists and higher temperatures. The Christmas market in December is a special experience, though it's much colder and quite crowded.