A signposted turn-off as you enter Port de Sant Miquel from the south loops 1km northeast around a headland to these underground caverns, once a smugglers' hideaway and now dramatically illuminated by coloured lights. Forty-minute tours in various languages run roughly every 30 minutes. After resurfacing, pause for a drink on the terrace bar and savour the panorama of sheer cliffs and deep-blue water.