Surrounded by forested karst peaks, this staggering cave system in Phong Nha-Ke Bang National Park extends for 31km, though most people only visit the first kilometre. The scale is breathtaking, as wooden staircases plunge into a cathedral-like space with vast alien-looking stalagmites and stalactites illuminated by large flood lights. Get here early to beat the crowds, as during peak times (early afternoon) tour guides shepherd groups using megaphones.
Paradise Cave is about 14km southwest of Son Trach. Electric buggies (per person one way/return 15,000/25,000d) ferry visitors from the car park to the entrance 1km away, or you can simply walk it. From the buggie drop-off, it's a further 600m-plus sweaty climb up to the cave entrance. There's an entry fee of 250,000d (125,000d for children).
To explore deep inside the cave beyond the barrier at the end (and with luck see the eyeless cave fish that are part of its ecosystem), book a 7km Paradise Cave tour (2,650,000d, minimum two people), which includes a swim through an underground river (there's a boat if you can't swim) and lunch under a light shaft. Bookings can be made through Phong Nha Farmstay and other accommodation options.