Grey didn't expect Sir Astarot would actually offer him such an opportunity. The secret worlds belonging to Magical Beasts aren't something humans can easily enter. In fact, Grey was almost certain that the number of humans that have been allowed to enter Magical Beast's secret worlds can be counted by one's fingers. Magical Beasts and humans have always been at odds, so there's no chance that they'll agree to let humans enter their secret worlds. Of course, there are cases like Grey's where a top Magical Beast expert will invite the person.
Magical Beasts and humans were two completely different races. So there are countless treasures that might not be usable for some Magical Beasts, but for humans, they were world-shaking treasures.
