It was great fun walking along the streets, enjoyingthe relaxing atmosphere!
请问句中的 walking 可以换成to walk 吗？
可以，且意思差不多（it为形式主语，其后的todo或doing为真实主语）。
It is funto do sth
It could be fun to watch them play. 看他们玩会非常有趣。
It’s fun to ski down a mountain. 滑雪下山非常有趣。
It's fun to be in a large city at Christmastime. 大城市圣诞期间很好玩。
It is more fun to go with someone than to go alone. 偕伴同去比自己一个人去好玩。
it is fundoing sth
It’s fun working for him. 为他工作非常有意思。
It’s no fun eating on your own. 一个人吃饭没意思。
It’s fun being taken to the zoo. 被带去看动物园真有意思。
It’s not much fun going to a party alone. 一个人一人去参加聚会没的意思是。