如果您想用英语表达“开始下山”的意思，可以说"Let's start the descent"。这句话的来源可能是源自人们日常生活中的实际经历，在登山或远足时经常会遇到这种情况。例句及其中文翻译如下：
Example:
We've reached the summit, let's start the descent now.
我们已经登上山顶了，现在开始下山吧。
The hike was strenuous, but the descent was a lot easier.
这次徒步旅行很艰难，但下山比较容易。
The trail was steep and spppery, so we had to take our time on the descent.
小路陡峭而且滑，所以我们在下山的时候必须慢慢来。