I live in a very old town which is surrounded by beautifulwoods.
我住在一个被美丽树木环绕的非常老的镇子里.
主句I live in a very old town
which is surrounded by beautifulwoods.是定语从句,修饰town
定语从句which is surrounded by beautifulwoods.采用了被动结构,因为是树木环绕镇子,而镇子只能被环绕,所以采用了be+done的一般被动语态,就是本句的is surrounded