The time came for Mu Lingxi's group to depart and head to Cloud Mist Ridge. This time, they were no longer as green as they were before.
Their past experience in their mission in the land of Echurid gave them a better idea about what kind of dangers they could possibly meet outside of their schoolyard.
The Cloud Mist Ridge is one of the rare places that are not accessible through simple means like the teleportation portals. Those who wish to venture the place will have to travel it on foot, though not literally on foot.
Basically, what it means is that Mu Lingxi and her friends have to painstakingly endure traveling back and forth to Cloud Mist Ridge without relying on any teleportation portals for easy access.
As the group already made their preparation for this journey, a carriage was already lying in wait for them as soon as they went out of the school.
BTW, Thestrals are from the Harry Potter series.
I think it was mentioned in the fifth book, "Order of the Phoenix".
During Luna and Harry's conversation.