Middle Earth: Shadow of Mordor - The White Rider - Liberate 30 slaves in 180 seconds while riding a caragor. [Bronze / 15G]

A great location for this is on the left side of the second map ("Sea of Nrnen", where the second half of the story takes place). If you have the Shadow Mount ability you can easily mount any Caragor from a distance.
Fast travel to the Forge Tower in the south-west. This will be your starting point. Also make sure it's daytime in your game! This is very important because the slave locations are different at night. You can advance the time by scrolling over a Forge Tower on your map.
The slaves are accompanied by one or two Uruks. Take them out to liberate the slaves.