The latest trailer for The Legend of Zelda: Tears of the Kingdom is adding more fuel to the fire of speculation that there's going to be a whole underground world to explore.
Fans have been theorizing about a big underworld in Tears of the Kingdom since it was first announced as simply the 'sequel to Breath of the Wild,' as that first trailer was focused on Link and Zelda delving into a cave where the mummified remains of someone - presumably Ganondorf - were sealed away. Since much of the surface world we've seen in Tears of the Kingdom appears pretty similar to the Hyrule we saw in Breath of the Wild, everyone's hopeful for a bit more - and an underground world in addition to all those locations in the sky might be just the ticket.
The latest trailer from the Nintendo Direct has a few hints at underground areas. There's a shot where a Hinox chases Link through a small cavern, but maybe you could justify that as simply being a cave on the larger overworld. There's a more compelling shot (opens in new tab) later on, where Link attacks a rock golem with a hammer - but while this cave is much bigger, it still seems feasible that it could just be another overworld area.
It's much more difficult to ignore the wide shot from near the start of the trailer, where we see a Bokoblin mining a stone (opens in new tab). At first glance, this looks like an outdoor area at night, but look again - all those 'trees' are actually mushrooms, and if you listen closely, you can hear the sounds in the area echoing, just as you'd expect in a massive underground complex.
As Zelda YouTuber Monster Maze notes, the little wandering flames in this shot are particularly interesting. They look exactly like spirits in the Twilight Realm of Twilight Princess. Whether or not there's a direct connection there - certainly the Zelda series often reuses imagery without building on previous lore - this does imply that this is some sort of alternate world unfriendly to non-monstrous creatures.
That leaves us with the idea that this is either a big underground area or, equally interesting, that this is a darkly mirrored underworld, which is a concept that constantly appears in Zelda games. Either way, it seems there might be a lot more to explore in Tears of the Kingdom than we previously thought.
The new trailer also hints at the return of ReDeads and the fate of Link's dead arm.