Torment: Tides of Numenera

In the bloom, you'll enter the Old Slave Block. Towards the far left of the map, after making your way down three series of steps, there will be a room you need to lockpick to enter. Immediately after, a man will try to slip past you. To earn this achievement, you must use your Speed stat pool to force him back in, after which he will be devoured by a Maw. A portal will open in this room, enter it and you'll earn the achievement.

Another solution is to let the slave go, then go into the room, but go by yourself. The Maw will kill you, but you will come back. The Maw will then be open, go through the portal, and the achievement will unlock.