This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
塸 combines 土 (earth) with 區, which likely contributes sound. The exact historical development is uncertain.
The left side is earth 土, and the right side is 區. Since the meaning is unclear, picture a mysterious mound of earth with a hidden compartment.
For オウ, imagine an old owl perched on the earth mound: owl -> オウ, and the owl guards the mysterious earth.