The best time to visit Spiez largely depends on your preferred activities, with the summer months of June to September offering the most pleasant weather for outdoor pursuits and the shoulder seasons providing good value.For those looking to enjoy the lake and surrounding mountains, the summer is ideal. Temperatures are warmer, making activities like swimming in Lake Thun, boat trips, and hiking in the nearby Niesen region very comfortable. This is also when all the cable cars and mountain railways are fully operational, providing easy access to panoramic views.If you're interested in a more relaxed trip with fewer crowds and potentially lower prices, consider visiting during the shoulder seasons of May or October. The weather is generally mild, suitable for walking and exploring the town, and you'll still experience the beautiful natural scenery without the peak season bustle.