Keya no Ohto

This guide to Keya no Ohto near Fukuoka opens at what local fishermen named the great gate: a cave-like portal cut into black basalt cliffs, formed as cooling lava cracked into six- and eight-sided columns and the sea slowly hollowed out the softer rock behind them. It traces the site's three centuries as a tourist draw, from a 1690s map through Taisho-era railway guidebooks, and the local legend that its far end leads to an undersea dragon king's palace. You'll hear why boats can only enter when the sea allows it. Listen for water dripping inside the cave as your boat passes through.