What wonders are hiding underground? Producer Marc Sanchez finds out what it’s like to explore one of the biggest networks of caves in the world — and scientists are still discovering unmapped branches. Marc will show us the wonders hidden underground at this national park in South Dakota and how tricky it can be to brave uncharted territory with only a headlamp to light the way. This episode is sponsored by Aunt Fannie’s (auntfannies.com/summer and coupon code BRAINS), Raddish (RaddishKids.com/brains and coupon code BRAINS), and Madison Reed (madison-reed.com and offer code BRAINSON). You can support the show at brainson.org/donate