North Korea possesses cross-border tunnels reaching beyond the demilitarized zone and into the territory of South Korea. Although the exact number of tunnels remains unknown, and in spite of the fact that they have never been used, these cross-border tunnels continue to pose a threat to South Korea’s national security.
I doubt if North Korea's ramshackle army could exploit the chaos potential of those tunnels--which could even handle large vehicles (plus air- and sea-landed forces)--without a massive dose of chemical weapons--and maybe not even then.
But the tunnels are a big part of North Korea's threat of invasion. If North Korea truly wants peace, giving them up would be a good symbol of intent.
And speaking of goodwill gestures, reaching out to offer aid to the victims of North Korean flooding seems like a no-brainer for America.