KanjiJLPT N1
Mount

mount, hill, knoll

Mnemonic

You crawl through a dark tunnel choked with wild grass, scraping your knees on tangled roots. When you finally emerge into sunlight, you're standing on a gentle mount — a soft, rounded mountain overlooking golden fields. The tunnel was the only way up this peaceful mound.
Additional thoughts
Picture the kanji structure: the tunnel enclosure wraps the outside, grass sits inside at the top, and mountain nestles at the bottom — like peering through a tunnel frame to see grass-covered earth atop a small hill.
Quick recall
Crawl through a tunnel of grass to stand atop a gentle mount, a miniature mountain.

Details

The keyword for 岡 is mount. This kanji refers to a small hill or elevated mound of land, typically one that is rounded and not particularly steep. It conveys the sense of a gentle rise in the terrain, less imposing than a full mountain. In modern Japanese, it appears most frequently in proper nouns such as place names and surnames, like Okayama or Fukuoka.
On'yomi
こう
Kun'yomi
おか