During the mission Locate Black Mask you’ll have to find the entrance to Lacey Towers. In order to do that, use the first fast travel point, then grapple on the rooftop.
Look for a building next to Lacey Tower (across the building with a huge neon sign Gotham Rail). On its rooftop you’ll have to defeat 3 cops. After defeating them, use Cryptographic Sequencer to decode broadcast. Two cops will walk out onto balcony on Lacey Tower. Glide towards them on the nearby balcony. Defeat them and the door behind them will unlock, and you will be able to enter Lacey Tower.