It has a lake, called Suwa-ko, which is not only famous as a sightseeing place, but also notorious for its dirty water.
The altitude of Suwa-city is 761m, and it is very comfortable in summer season. However, in winter, it is colder than Matsumoto-city. Sometimes Suwa-ko is frozen and a mysterious phenomenon called "Omiwatari" appears. This is not an annual event.
Suwa-ko is well known for its fireworks festival. It is held on the 15th of August every year. The fireworks are very beautiful and have a powerful sound. They really impress to the crowds. The number of spectators is approximately 450,000. It causes heavy traffic jams for all of Suwa-city. You can see the fireworks on the website below on demand.(Sorry, this website is written only Japanese.)