Pretty straight forward but there are two options for unlocking this achievement.
1. Get a character to level 10 Survival and purchase the perk called Explorer’s Instinct. This will immediately unlock the achievement regardless of how many locations you have actually visited.
2. Actually go to every location... obviously. I don’t want to spoil stuff for those who just want to get a quick overview so I will include some spoilers below.
How many locations are there?
What does the full map look like?