However, far from being the abode of a comic book superhero, this deep cavern hidden in limestone hills close to the county's eastern border makes a fascinating, if challenging, half-day excursion and is certainly one of the most unusual ways to spend a day out in Taiwan.

There are several other 'bat caves' dotted around the island, but most are either fenced off and out of bounds to the public, or are only seasonally occupied by those fascinating flying mammals. The remainder have been abandoned for remoter locales after tourist traffic frightened the inhabitants away long ago.

All of them, that is, except Guansi Bat Cave, which remains home to countless numbers of the little critters, although visiting their dark home isn't exactly a walk in the park.

The bat cave has been something of an attraction for several decades, and the little road to the trailhead is clearly signposted off the Luoma﹝羅馬﹞ Highway (county route 118), which connects Guansi with the North Cross-island Highway, 35 kilometers to the east. Turn off route 118 close to the 32.5 kilometer road marker (a wooden sign points out the way to the cave).

The lane is exceptionally narrow in places, but (keeping left at the fork) it's not too long before it reaches a small parking area beside a public W.C. Leaving the vehicle here, a concrete track continues ahead, steeply uphill, until a clear, stepped path on the right climbs the hillside towards the cave. As I climbed with my three companions, the sky overhead was overcast and threatened rain.

It had poured overnight and the wet path was treacherously slippery. The stone slabs of the path were bordered with low hummocky plants studded with pretty tiny trumpet flowers of palest lilac.

Gingerly placing our feet as we climbed, it was less than ten minutes before the path reached its highest point and started descending. Almost at once, a tall, sheer cliff of weathered limestone reared up on the left, its base pierced by a large black hole. This cave was inaccessible after a few meters, but following the trail steeply downhill a minute or two further, another dark cavity in the rock appeared, with the Chinese characters '出口' ('exit') painted in red paint beside it. This is actually now the main entrance to the system, after the original entrance nearby was closed.

Getting out torches and leaving backpacks at the mouth of the cave, we entered, only to find a vertical chimney about 20 meters in depth immediately inside. A long and awkward rope ladder is permanently fixed to the rock, and after lots of struggling and puffing, we were standing at the bottom, at the start of a long, steeply sloping passage which dives down into the bowels of the Earth.

This tricky bit over, the next stage proved a much easier walk through a natural cavern whose roof soon rose high above our heads. Entering a large cave chamber about five minutes in, another long rope ladder gave access into a chamber above at the far end of this huge cavern for further exploration.

Hearing the squeaking of countless bats over to the left, however, we stumbled in the direction of the sound, down a branching passage, and shone our torches into a wide crack in the wall. The light startled into flight a cloud of bats which began madly circling in the torchlight, several escaping the chamber and brushing past our ears as they darted for the entrance.

Having unintentionally caused mass panic in the bat chamber, we quickly turned our torches in the opposite direction and took a look at the rest of the cave. Climbing down the rope ladder at the entrance to the cavern had been a challenge, but the second ladder was a tougher climb still, and after a quick try it was clear that going any further would be a dangerous proposition. We'd already disturbed the bats quite enough, anyway.

Safely back at the entrance to the bat cave, we still had one other place in our sights: the so-called Blue Green Waterfall (碧綠瀑布). Reached by a steep and extremely muddy trail down the hillside below the cave entrance, the waterfall is unlike any other I know in Taiwan.

Walking the last few meters up to the waterfall stepping on dry rocks in the bed of the fast-flowing stream, the waterfall cliff came into view ahead, but curiously it was completely dry. Only when we reached the plunge pool at the base of the falls did we discover the stream gushing out a small black hole at the base of the cliff.

The water in the stream disappears upstream into a sinkhole, to emerge back into daylight only here, at the foot of the waterfall. It's a bizarre sight, and, for Taiwan a unique one.