Experience one of the most unique things to do in Lan Ha Bay: kayaking or taking a bamboo boat through the Dark & Bright Cave (Hang Sang Toi). This fascinating sea cave involves paddling through a low natural tunnel carved through a towering limestone karst. The "Bright" cave section is a short, light-filled tunnel leading to a stunning, enclosed lagoon surrounded by sheer cliffs – a hidden paradise.

The "Dark" cave section is longer and often inaccessible depending on the tide. The journey through the Bright Cave tunnel into the hidden lagoon is a highlight of many Lan Ha Bay cruise itineraries. Paddling through the archway and emerging into the quiet, jungle-clad lagoon offers a magical sense of discovery and showcases the unique geology of the area.