Find the hidden access to the mansion grounds in Ep. 10: Legacy
Battlefield Hardline SOCIAL CLIMBER Achievement / Trophy Guide
To find the hidden access you need to use the grappling hook. Equip it at the beginning of the episode and make your way through the level. Stay left on the island and pass the pool area.
Just after you see a road sign on the right you can see a path on the left. Take it, and walk until you see two enemies. Take them out and look up to see the two platforms you need to climb. Equip your grappling hook and you have used the hidden access to the mansion.