The so-called “eternal flame falls” is a waterfalls of Shale Creek in the southeast corner of Chestnut Ridge Park in an area known as the Shale Creek Preserve. A grotto on the right side of the falls (as you are facing it) has several fissures through which methane gas escapes.
There are lots of fissures in the creek bed through which methane gas escapes, and you’ll smell it as you approach the falls, but the others can’t be set aflame because they are exposed to dissipation by the air currents or are under water (look for rising bubbles.)
Contrary to its name, however, the Eternal Flame it is not always on flame but the escaping gas can usually be lighted with a barbeque lighter, so bring one with you in case the flame has gone out when you get there.
The trail begins on Seufert Road, just past the intersection of Seufert Road and Route 277. The trail is only 1.5 miles round trip. However, it appears from the trailhead kiosk that there is a partially marked trail that leads back to the main area of Chestnut Ridge Park (near the casino, which, like the eternal flame, despite its name is not a gambling casino but rather a park lodge.)
The trail heads northeast and after crossing shale creek it climbs a rise to reach the north rim of the shale creek gorge. The trail then turns northwest. Just ahead you’ll find the eastern end of a spur trail (marked Trail Jct 2 on the map.) It appears that this spur trail goes in a semicircular route and meets up with the main trail again (marked Trail Jct 2 on the map) just as the main trail turns southeast to descend to the creek bed.
After turning northwest, the trail climbs slightly and then begins to descend. The trail passes near the edge of the north rim of the gorge. The area of the creek that you can see below is the location of the eternal flame falls. You’ll often see others at the bottom of the gorge from this vantage point.
As mentioned, at the furthest northwest portion of the main trail, there is another junction with the spur trail, shown as Trail Jct 2 on the map.
The main trail descends to the creek and then turns southeast as it heads upstream to the falls.