Find a way to the surface is a mission objective in Assassin's Creed Unity: Dead Kings (ACU:DK)
"Find a way to the surface" is a mission objective in Sequence 13 / Memory 02: The Book Thief
Walkthrough
Head into the central structure and start climbing upwards. This will lead Arno out into the Windmill District and into a small fight. Once you dealt with them, you will need to Leon once again.
