First look at Marvel's Agatha spin-off teases a very significant location, and links to a major MCU character

gamesradar.com:

Marvel has unleashed a special behind-the-scenes look at the upcoming WandaVision spin-off Agatha: Darkhold Diaries, and fans have already spotted a major MCU Easter egg.

Soon after the clip was posted to Twitter, eagle-eyed fans quickly drew attention to one shot where Agatha Harkness, played by Kathryn Hahn, is seen walking on a cobble-stone path in a dark woodland, which looks very similar to the Witches' Road. One viewer posted the screenshot to Reddit stating, "I'm calling it now, this scene takes place on the Witches' Road", while other users in the thread appear to agree. 

What is the Witches' Road? Even if you consider yourself a superhero aficionado, you may not have heard of the mystery location as it has not yet appeared in the MCU. First introduced in a Scarlet Witch comic back in 2016, the Witches' Road is a plane of existence where only sorcerers can tread. With that, fans are finding the shot extra exciting, because it hints at a possible return from a beloved, and presumed dead, MCU character.

Further down in the Reddit chain, another user explains that in the book, "Agatha guides Wanda through the Witches' Road to find why witchcraft is weakening. The goddess Witchcraft resides here. In the book, someone related to Wanda takes on the mantle of the goddess, but I'm wondering if the MCU will do its own thing and make Wanda become the goddess at some point."

If the characters spotted in the featurette are on Witches' Road, it'd support the well-spread theory that Heartstopper's Joe Locke is playing Wiccan, the magic-wielding reincarnation of one of Scarlet Witch and Vision's sons. For now, Marvel has suggested that Locke's character is simply a familiar, but given familiars aren't typically sorcerers