The entrance to Ondal cave, which is South Korea Natural Monument No.261 (<a href="https://ko.wikipedia.org/wiki/%EC%98%A8%EB%8B%AC%EB%8F%99%EA%B5%B4" class="extiw" title="ko:온달동굴">ko:온달동굴</a>)
Integral
CC BY-SA 2.0 kr
<span class="int-own-work" lang="en">Own work</span>