The garage is completely wrecked. It is inhabited by raiders and has functional Protectron pods with an access terminal nearby. The lower floors house two elevators, one of which takes the Sole Survivor to an unsafe ledge high in the wrecked scaffolding of the building, the other takes them to a walkway that leads to an alternate entrance to the Commonwealth Bank.
This elevator also leads to some stairs that can allow the player character to access the highway. The ground floor of the garage also contains the back entrance to the Haymarket Mall. Coming from the mall, the garage is accessible with a key found on a raider on the second level.
Sometimes the raiders and Protectrons will be dead upon arrival.
Congress Street garage appears only in Fallout 4.
If the player character attempts to open the hatch while the elevator is in operation, there is a chance the player character may fall through the ground to their death. [verified]