Ubisoft released an 11-minute gameplay video for Assassin’s Creed Unity at GamesCom 2014.
In this video, which also features commentary from creative director Alex Amancio, Assassin Arno Dorian is tasked with taking down a corrupt Templar named Sivert inside the Notre Dame Cathedral. The catch is that the church is heavily guarded and because battles are more difficult now, the player is forced to be creative and look for other ways to get in. This mission type is called the “black box” because it gives you complete freedom to carry out your task in any way you want to.
That means you can choose between finding an entrance from the roof-top, tailing and assassinating a character who is going out to meet your target, or retrieving the keys from some thieves to allow you access through windows. Note that Amancio said that there are 10 possible entrances to the cathedral and you need just one.