to swim in Kunming Lake is a great pleasure

to swim in Kunming Lake is a great pleasure
这里to swim可以用swimming代替.只不过swimming侧重于普遍行为,to swim侧重与一次行为,或表示想要的意思.
I like swimming是我喜欢游泳（这种活动）,i like to swim.我想去游泳.
swimming is a great pleasure in Kunming Lake,或swimming in Kunming Lake is a great pleasure.都行.只是强调的语气有一点不同.
在这句中不是in kunming lake作主语,而是to swim in kunming lake为主语,is是谓语.
great不能用very代替,因为表示“很”的意思时very只是副词,后面要加个形容词.
very作为形容词的话,表示“正好”的意思.如
That's the very thing I've been looking for.
那正是我要找的东西.