例如Some cities have these extremely large parks, where there are wildlife, grasses, and flowers.这句话有语法错误吗？
这句话没有错啊。where引导的定语从句只要有完整的结构（如主谓、主谓宾、主系表）即可，并不排斥there be句型。
不妨先假设这样两句话：
Some cities have these extremely large parks. People can enjoy themselves in these parks in their spare time.
用定语从句合并为一句话，就是：Some cities have these extremely large parks, in which people can enjoy themselves in their spare time.
或：Some cities have these extremely large parks, where people can enjoy themselves in their spare time.
再回到你所问的句子，也可先拆成两句话：
Some cities have these extremely large parks. There are wildlife, grasses, and flowers in these parks.
同样用定语从句合并为一句话，就是：Some cities have these extremely large parks, in which there are wildlife, grasses, and flowers.
或：Some cities have these extremely large parks, where there are wildlife, grasses, and flowers.
We climbed to the top of the mountain, where there is a large temple.
