Naturally, the best weather we encountered was on our last [half] day in Matsu. Excavation for Nangan’s [南竿] Dahan [大漢] Stronghold began in 1975 by soldiers using basic equipment. Work was completed on March 29, 1980.
The Stronghold is divided into three levels of tunnels:
The upper level served as army company headquarters, the middle level contained a living area and a reserve machine-gun emplacement, and the bottom level housed four 90-millimeter anti-aircraft gun emplacements, a briefing room, lounge, arsenal, and storage room.
The total length of the tunnel network is 430 meters, they are 1.5 meters wide, and 2 meters high.
Renovation work on the tunnels was completed in 2006 by the Matsu National Scenic Area Administration.
Sadly, this was the best of my tunnel pictures:
The Daily Bubble Tea 
The top one is a nice pic. Is the military still using this, or is it a museum now?
Patrick, it is strictly a museum now.