Siju Caves cuts through limestone hills in the South Garo Hills and holds one of the longest cave systems in the country, with chambers large enough to house a resident bat colony and passages that river water has carved over centuries. It's a proper caving trip rather than a quick photo stop, best suited to travellers who want adventure and geology over easy sightseeing, and it works well as a detour on a wider Garo Hills itinerary rather than a standalone destination.