Peru's Tambopata National Reserve has long been a destination for travelers bent on humping through the jungle with their DSLRs to take vivid and colorful pictures of scarlet macaws and toucans. This remote swath of jungle is thick with animals – red howler and capuchin monkeys fight in the trees – but the most exciting bit of local fauna can only be flushed at night. Caimans, the nocturnal Amazonian crocs that jostle with giant otters, anacondas, and jaguars for position atop the Amazon food chain, are native to the region and easy enough to find for guides equipped with floodlights that reflect in the predators' shifty eyes. The 7-foot-long spectacled caiman and the rarer (and beefier) black caiman – at 800 pounds, the largest predator of the Amazon Basin – are the reserve's toothiest attraction.

Tours begin at the reserve's lodges with a hike towards the river jetty through a thick darkness enforced by the pitch-black rain forest canopy. As torches dart across the trail, trekkers catch glimpses of colorful tree frogs, burrowing tarantulas, and emerald tree boas coiling in the branches. The trees move, but a bit more slowly. Walking palms and strangler figs spread slowly across the forest, casting reptilian shadows across the riverbanks.

Guests and guides climb into narrow-hulled, wooden riverboats that motor upstream to an undisturbed stretch of the Tambopata River, an offshoot of the wider Madre de Dios. A guide cuts the engine and the vessel begins to drift downriver as passengers look at the edges of the forest and the forest looks back. Heat lightning exposes caimans lolling on the sandbars.

Flashlights are the absolute must-pack for a trip: Caimans' eyes possess a strange property that makes them flash bloodred when exposed to light. If they are concentrated in high enough their numbers – finding 20 or so large individuals hanging out together is not uncommon – this can result in a menacing ruby constellation. The species tend to vary according to the body of water they're in: White caimans cruise the main river while black caimans haunt more slow-moving streams and oxbow lakes, waiting patiently to ambush ill-fated capybaras. What visitors need to know is that both species will approach boats to check out their occupants. The feeling of exposure as these massive beasts, gaping on the murky shore, turn to advance towards the boat is both chilling and exciting. To be hunted is to be truly in the jungle.

It comes as a bit of a relief when the engine roars back to life.

More information: Tambopata National Reserve is reached via the Amazonian city of Puerto Maldonado, a 90-minute flight east of Lima. From there, it's a short (albeit rocky) bus transfer and a two-and-a-half-hour boat ride to Refugio Amazonas. Rates at the lodge start from $375 for a two-night stay, which includes transfers, meals, and caiman watching.