Eternal Flame Falls, at Chestnut Ridge Park in New York, is a small waterfall in front of a small grotto that emits natural gas, which can be lit to produce a small flame. This flame is visible nearly year round, although it can be extinguished and must occasionally be re-lit.

See a video clip of this amazing phenomenon here:

https://commons.wikimedia.org/wiki/File:Burning_Eternal_Flame_Falls_Chestnut_Ridge_Park_NY_2025-09.webm