This is from the Year 2 Season 4 content "Forsaken." It is located in the large citadel in the landing area of the Dreaming City.
Similar to Escalation Protocol, this allows you to bring a fireteam of up to 3 people into an instance with other random players. Unlike the original EP, though, this is much more manageable with fewer people. 3-4 players at 540+ power can easily clear all tiers of the Blind Well.
You can ask random players in your instance to invite your friends to expand the number of players up to 9 between the fireteams.
Blind Well is one way to get a Seed of Light to open your other Super nodes.