Watership Down is about a group of rabbits setting out from the old, known home to find or make a better world out there somewhere in the unknown. In other words, exploration here is often about facing fears and finding the perfect place to set down some roots (or use them to hold up your living room). Almost every episode of their journey involves some form of exploration: they leave Sandleford and hop across unknown parts of England; find a new (and weird) warren; raid a new farm; send two expeditions to a new (and dangerous) warren. Really, the only time Hazel's rabbits aren't exploring is when they're protecting their home from Woundwort's army, but that's because they've already found their spot of earth—now it's time to defend it.
In Watership Down, exploration is a tool. The ultimate goal of all exploration is to find a place to stay so you don't have to explore any more.
Only human-built landscapes are truly new and dangerous to the rabbits.