A neat little Easter egg found in Fallout 4 may connect Bethesda's post-apocalyptic open-world videogame franchise to its fantasy-themed open-world videogame franchise, The Elder Scrolls.
Mild SPOILERS that are not related to main story quest of Fallout 4 may follow.
If your Vault-dweller choses to ally himself or herself with the Brotherhood of Steel, you may find yourself on board the faction's airship, the Pyrdwen. While investigating the Pyrdwen, you may come across a research station where various flora and fauna are being examined. Most of these species are common enough in the Commonwealth, but there is one exception.
As Kotaku reported in more detail, this experimental plant is not found on the ground of the Wasteland. A closer look at the plant reveals a strong visual similarity to the Nirnroot plant found in The Elder Scrolls games. If the visual similarity alone isn't enough, the computer logs of the researchers – labeled "NRT" – describe common traits between the two plants, including that they both glow and grow near water.
So could the universe of Fallout be connected to The Elder Scrolls? Maybe, but the Fallout games are known for their humor, so I'd take this more as a wink and a nod than as a canonical prelude to a crossover.
What makes this particular Easter egg and theory fun is that it positions post-apocalyptic Fallout as a predecessor to the lush fantasy world of The Elder Scrolls. The radiation from the nuclear event that began the Fallout universe could be taken as an explanation for why the Nirnroot glows, and why the Elder Scrolls universe is inhabited by cat-people and lizard-people.
If you're interested in Fallout 4, be sure to check out game review.