According to google searches, the Jinping Underground Laboratories are the "deepest" building or buildings constructed, reaching 7900 feet (2400 metre) below the surface.... However, the surface in question is a mountain. While that does classify as underground, it highlights a flaw in the question of the deepest underground building.
I can't seem to find the lowest building in the world though, or the deepest in relation to depth within the earth's crust.
What is the lowest point below sea level that we have built where a human can go? I imagine this is likely another laboratory. But where would a building of this description be?