It was torture seeing him dig up my grass.

【参考译文】

看他在我的草地上胡刨乱挖真是一种折磨。

【参考解析】

咱们看看《柯林斯高阶》的解析：

torture: N-UNCOUNT 折磨;痛苦;苦恼;引起痛苦(或苦恼)的事物

If you say that something is torture or a torture, you mean that it causes you great mental or physical suffering.

Waiting for the result was torture. 等待结果的过程是一种折磨。

实际上你的句子相比上面的例句只不过用了形式主语 it 而已，即:

It was torture seeing him dig up my grass.

=Seeing him dig up my grass was (a) torture.

咱们熟悉的还有：

It is no use / fun doing sth. Use 与 fun 就都是名词。