For travellers seeking thrills and adventure alongside cave exploration, Dark Cave (Hang Toi) offers a unique and action-packed experience in Phong Nha. Unlike the boat journey of Phong Nha Cave or the boardwalks of Paradise Cave, Dark Cave is all about getting wet, muddy, and exhilarated. The adventure often begins with an exciting zipline ride across the Chay River to reach the cave's entrance, setting the tone for the activities ahead.

Once inside, equipped with helmets and headlamps as your only light source, you'll navigate through parts of the unlit cave, wading or swimming through cool underground river sections. The highlight for many is reaching a large chamber filled with thick, gooey mud, where you can enjoy a fun and therapeutic mud bath, floating effortlessly in the dense mixture. Afterwards, you rinse off in the river inside the cave before kayaking back across the Chay River, often with opportunities for zip-lining into the water or other water-based games near the cave entrance.

Dark Cave provides a completely different kind of cave experience – focusing on adventure, physical activity, and fun rather than just admiring formations (though the cave itself is impressive). It's essential to wear swimwear and be prepared to get thoroughly wet and muddy. Due to its adventurous nature, it's popular with younger travellers and those seeking an adrenaline rush combined with their cave exploration in Phong Nha.