Here's an interesting post about Hezbollah's Pyongyang-built and engineered tunnel and bunker system
Massive underground fortifications, built with Pyongyang’s knowhow, have been key to Hezbollah’s ability to fight Israel – and preview the difficulties of any assault on North Korea.
thediplomat.com
by 2006 estimated to have over 600 ammunition and weapons bunkers fortified eight or more meters underground – alongside better fortified command bunkers constructed to a depth of 40 meters using poured concrete. By that time there were at least ten Korean-built tunnel and bunker networks in southern Lebanon – each with dozens of command bunkers, which in turn were each divided into several rooms.
When war broke out that year, Hezbollah’s rocket artillery systems were often deployed from firing pits five meters deep, with foot-thick poured concrete frames reinforced with blast walls and covered with sandbags and thermal blankets, minimizing positions’ heat signatures and making them highly resilient to Israeli air or artillery strikes. North Korean-style tunnels thus served as a force multiplier
That's 2006, 18 years ago. By now god knows how many miles more they had dug.
Looking at Hamas basically intact inside Gaza, we're looking at a larger acope of work here. Unlike Gaza, manpower and supply is a non-issue for Hezbollah as their supply line are open from Iraq.
The Israelis will waste so many bombs and artillery shells trying to neutralize those bunkers. and it's not even going to dent much.
Ukraine's going to be pissed when they realize that their shells are again going to be diverted to israel.