Go to Alluris and eventually you will get a quest event where you are asked to take medicine to the other town on the main road.
After delivering that, a quest may appear in that town to make a delivery of other items to another town. This town is not on the main road and can be accessed either by going to the front gate as a random event in the mountains (you need 1000 gold to get in. You will keep the money but they dont let you in if you dont have money.), or by going into the cave on the main road and going to the deepest part of the cave, from there an event with a staircase leading up can take you to this town or the Alluris undercity randomly. Going via the cave bypasses the 1000 gold entry requirement, but is more dangerous and might take you to the wrong place.
After dropping that off, hang out in the dwarven city and you'll eventually get the last quest of this chain to deliver weapons to the elf city. It helps to have the barrel before going here, this is obtained via an event on the main road where you find a frightened farmer. Choose to save the farmer and defeat the monster to be given the barrel it was in. Next stop is the forest, then heading to the deeper part of the forest. Here you will eventually find a waterfall, choose to jump off; with the barrel you take no penalty, without you will still make it but take a huge 50 damage hit that can kill you. Simply make the delivery here and the achievement is yours.