doors
闔 centers on doors, specifically the entire door or gate structure, often implying closure or the whole set of doors.
闔 combines 門 (gate) with 盍, which likely contributes the sound and possibly the idea of covering or closing, as 盍 itself can mean 'to cover'.
The gate 門 encloses 盍, which looks like a lid over a dish. Picture a large gate with a cover that closes completely, representing the whole door.
For コウ, imagine a gate that closes with a loud 'ko' sound, like a heavy door shutting: 'ko' -> コウ, and the gate is the door.