This 700m of sea tunnel took three laborious years to carve out with many soldiers losing their lives in the process. Completed in 1971, it was used as a hiding place for up to 120 small boats, protecting them from potential aerial attack. Visits are free on foot (low tide only), or you can pay to float or kayak through the four surprisingly wide, criss-crossed channels.
Across a small, pebble beach is the entrance to the smaller, hand-cut tunnels of the Dahan Stronghold. There's nothing inside, but forking right at the first bifurcation allows you to loop back to the Nangan Visitor Centre via a path that climbs the rocks then descends through pretty woodland.
From April to September, there are evening boat rides six times nightly in the Beihai tunnels giving a fair chance of seeing blue tears: the tunnel lighting is briefly extinguished and, when the waters are stirred with the oars, you'll hopefully see a faint blue glow. Demand can be high so it's worth pre-booking: call 083-622 177 before 4.30pm or, better, prepay at the tunnel counter.
