Enid opened the entrance to the hidden world, William immediately put some strength into his right leg and quietly entered. According to Agrustu's words, he had to climb the huge mountain he saw in front of him and then go inside. Just like the volcanoes he had been in before.
Taking a few steps, William reached the top of the mountain in a few seconds and saw the giant tree. Up until this region, no region was included in the scope of the hidden world. This place was just a huge illusion shield created by Enid and the others. There were no restrictions around the tree, the part that even Enid couldn't reach. William just had to go straight.
When William looked behind him, he saw that several mages had already entered the shield and started to run up the mountain with mitigating(lightening) spells. Not wanting to lose his speed advantage, William took a few more steps and came to the actual entrance to the hidden world.