Many travelers agree that the best time to come to The Netherlands is during the warmer months. Anytime between spring and summer is a good time to go, but you can also have a good time when you visit Leiden in the fall. If you visit during the spring or summer you will get much longer days of sunlight which will allow you to stay out later and do more. Also, the city really comes alive in the warmer months. After being couped up all winter, most of the locals are just itching to get out and do things. If you visit in the fall, people will still be out doing things, but it will also be a little bit cooler. Though the temperature never gets too hot, it's still nice for it to be a little bit cooler out. Also, in the fall there are many different festivals going on all the time. When you go to Leiden you should pack at least a pair of pants and a light jacket. Though it may be warmer in the daytime, at night the temperature can dip quite a bit, and you don't want to be left shivering. If you go in the winter, you should definitely pack warm clothes like pants, sweatshirts, and jackets.