For the truly adventurous, Phong Nha is the gateway to incredible multi-day adventure caving expeditions. Tours operated by licensed companies (like Oxalis Adventure) take small groups trekking through remote jungles and exploring vast, undeveloped cave systems like the Tu Lan Cave System or Hang En Cave (the world's third-largest cave).

These challenging trips involve hiking, swimming through underground rivers, scrambling over rocks, and often camping inside caves or in the jungle. While requiring a higher level of fitness and budget, these Phong Nha caving tours offer unparalleled wilderness and cave exploration experiences.