Big South Fork, TN/KY
Follow fireflies to sandstone arches.
During the day, hikers come to the Big South Fork for its deep, winding gorges and imposing sandstone bluffs. But on summer nights with a new moon, the main attraction is something much more dazzling: fireflies. From the Twin Arches trailhead, hike south .7 mile to the Twin Arches–North and South Arch (51 and 70 feet tall, respectively), two of the largest natural bridges in the east. Watch the fireflies light up the sandstone walls. They don’t blink randomly; different patterns and sequences indicate species, gender, territoriality, and even mating status. Continue east on the 4.6-mile Twin Arches Loop Trail, passing rustic Charit Creek Lodge as you close the loop. (423) 286-7275; nps.gov/biso
Enjoy midhike milk and cookies on the Charit Creek Lodge porch. Call ahead. (865) 429-5704; charitcreek.com.
From Oneida, TN, take TN 297 west 19 miles to TN 154, turn right, and drive 1.5 miles to Divide Road. Turn right again, and make another quick right onto Twin Arches Rd. It’s two miles to the trailhead.