It was another bridge to the elemental planes enhanced. While it was not the last, Walker felt that he was able to learn a lot about what he had just found. Midnight and Onyx had managed to understand a little more about what the elemental planes were and what the bridges were.
Since they could see and sense the changes in the world because of the added manas and even see that both could affect the dungeons it was very clear how all three would work together. It also made both of them consider how they would be able to use all of this in their growth along with others.
For Midnight, she was resting on the idea that she would be able to bring the younger dragon hatchlings to safer dungeons like this. They would be able to handle the higher amounts of mana because dragons naturally were more resistant to the manas they had affinities for. However, where things would really be important was that they would be able to get the best mana possible for them to grow.