Spoiler warning for The Defenders! There are a lot of mysteries for the Defenders to solve in their eight-episode series, and the largest amongst them has to do with a giant hole beneath the Midland Financial Circle building. Investigating an architect's background may seem like it's below the combined talents of four superheroes, but the secrets in John Raymond's schematics speak for themselves. What's in the hole on The Defenders, why was it built in the first place, and who had the resources to dig it out?
While The Defenders is a show about New York superheroes, there's another city that the characters can't stop talking about. The main plot of The Defenders revolves around K'un-Lun, the ancient, mystical city where Danny Rand grew up and trained. Between Iron Fist trying to save K'un-Lun and The Hand trying to raid it and rob it of a mysterious substance, it's a vitally important location to The Defenders. The Hand seems to believe digging a giant hole underneath New York City is going to bring them closer to K'un-Lun, but how? In Iron Fist, Danny Rand attempted to find the home he left by by hiking through a mountain range in Asia and coming across a gate to the mystical city. So what does a giant hole in the ground have to do with The Hand's plan?
In Episode 7, it's revealed that the hole beneath Midland Financial Circle seems to be an alternate route to K'un-Lun. When Iron Fist is taken there, it becomes clear why The Hand has been referring to him as a key. The base of the hole is an excavation site, covering a stone slab. Etched in the slab is text in the language of K'un-Lun. While Iron Fist can't read the text on the slab, it's clear that The Hand believes that the slab leads the way back there. It seems that the organization is placing a lot of faith in a giant rock, but the excavation site also features bones of a creature that could only be found in K'un-Lun.
At the end of the show's penultimate episode, Danny comes across a giant skeleton. He finds himself beneath a giant ribcage and he soon discovers that these bones aren't just an oversized dinosaur fossil. He's beneath the bones of a dragon — just like the dragon he's mocked by Luke for claiming he fought. That dragon seems to prove that there is a portal between K'un-Lun and the base of the giant hole, as it's doubtful that The Hand managed to sneak a dragon through New York City and throw it down the hole themselves.
Everything about Midland Financial Circle, from the founding of the company to the building of the skyscraper, was all a front for excavating the fossil of a dragon. The Hand's seemingly endless resources make them a terrifying foe, and nearly impossible to bring down. But they've never faced the Defenders before.