Shadow Chamber (XCOM2)
The Shadow Chamber is a special research lab for the highest priority and most complex subjects: you need it to examine the strange substance sample you captured at one of the earliest Blacksite raids, and the Codex 'brain' you recovered from that strange electromagnetic alien.
It is of similar utility and story requirement to the Hyperwave Uplink. Once built, it tells you the composition and total number of the enemies in a mission on the Hologlobe: study this information well to see if you need to bring any special weapons or soldiers with certain perks, such as if facing a heavily mechanized ADVENT/alien force. It has no slot to benefit from a staffed Engineer.