cellar
窖 centers on an underground storage space: a cellar or pit used for keeping things cool and preserved.
窖 combines 穴 (hole, cave) with 告, which likely contributes the sound. The character originally referred to an underground storage pit or cellar.
The top 穴 is a hole or cave, and the bottom 告 looks like a container with a lid. Picture a hole in the ground with a covered storage area: a cellar.
For コウ, imagine a cold cellar where you store kohlrabi: kohl -> コウ, and the vegetable stays fresh underground.