a small, deep swimming pool, especially one containing cold water for cooling yourself down after going in a sauna (= a small wooden room or building that is heated to a high temperature)

Should I take a warm shower or jump into the plunge pool filled with ice cold water? 我应该洗个热水澡还是该跳进装满冰水的浴池？

Some of the hotel rooms have private plunge pools.

a pool of water at the bottom of a waterfall (= water, especially from a river or stream, dropping from a higher to a lower point)

The walk ended with a refreshing dip in a waterfall plunge pool. 健步出行以在瀑布下的水潭中畅游而告终。

There are several natural plunge pools between the trees.